Don't leave stray Mercury directories in tests.

tests/Mmake.common:
    Bootchecks in the csharp and java grades, which use mmc --make
    and --use-subdirs, have traditionally left all the Mercury directories
    they constructed in tests/*. These screwed up any subsequent bootchecks
    in other grades, because the mere presence of those directories
    told the compiler to put their results in there, which was not always
    what was wanted.

    Fix this by

    - deleting any Mercury directories before we start runtests in a test
      directory,

    - deleting any Mercury directories after runtests succeeds in a test
      directory, and

    - rename any Mercury directories after runtests fails in a test
      directory, to Mercury.failed.

    This last part allows any failures to be investigated and debugged,
    without interfering with later bootchecks. (Though those later bootchecks
    will delete any Mercury.failed directories, so they should be moved
    elsewhere first if they may be needed later.)

tools/bootcheck:
    Delete the temporary code that helped me track down this issue
    and to conform its fix.

    Fix too-long lines.

tests/Mmake.common

@@ -360,6 +360,7 @@ start_runtests_local:
 		rm -f *.trans_opt *.trans_opt_date > /dev/null 2>&1; \
 		rm -f .mercury_trace_counts* > /dev/null 2>&1; \
 		rm -f .date* > /dev/null 2>&1; \
+		rm -rf Mercury > /dev/null 2>&1; \
 	fi
 	@> FAILED_TESTS
 
@@ -396,6 +397,7 @@ start_runtests_local:
 TEST_LOGS = $(THIS_DIR_TESTS_TO_RUN:%=%.log)
 runtests_local:
 	+@ \
+	/bin/rm -fr Mercury lib/Mercury > /dev/null 2>&1; \
 	mmake -k $(MAYBE_J1) $(TEST_LOGS); \
 	touch DUMMY.log; \
 	cat *.log > $(ERROR_OUTPUT_FILE); \
@@ -405,9 +407,18 @@ runtests_local:
 		echo cleaning up the directory after the tests; \
 		mmake $(RM_JFACTOR) realclean_local > /dev/null 2>&1; \
 		rm core > /dev/null 2>&1; \
+		/bin/rm -fr Mercury lib/Mercury > /dev/null 2>&1; \
 		touch CLEAN; \
 	else \
 		echo "FAILED tests in $(THIS_DIR) $(PARAMS_MSG)"; \
+		/bin/rm -fr Mercury.failed lib/Mercury.failed \
+			> /dev/null 2>&1; \
+		if test -d Mercury; then \
+			mv -f Mercury Mercury.failed; \
+		fi; \
+		if test -d lib/Mercury; then \
+			mv -f lib/Mercury lib/Mercury.failed; \
+		fi; \
 		exit 1; \
 	fi
 

tools/bootcheck

@@ -1063,12 +1063,14 @@ then
         if test -f "${root}"/Mmake.stage.mdbcomp.params
         then
             /bin/rm -f mdbcomp/Mmake.mdbcomp.params
-            cp "${root}"/Mmake.stage.mdbcomp.params mdbcomp/Mmake.mdbcomp.params
+            cp "${root}"/Mmake.stage.mdbcomp.params \
+                mdbcomp/Mmake.mdbcomp.params
         fi
         if test -f "${root}"/Mmake.stage.browser.params
         then
             /bin/rm -f browser/Mmake.browser.params
-            cp "${root}"/Mmake.stage.browser.params browser/Mmake.browser.params
+            cp "${root}"/Mmake.stage.browser.params \
+                browser/Mmake.browser.params
         fi
         if test -f "${root}"/Mmake.stage.ssdb.params
         then
@@ -1084,7 +1086,8 @@ then
         if test -f "${root}"/Mmake.stage.deep.params
         then
             /bin/rm -f deep_profiler/Mmake.deep.params
-            cp "${root}"/Mmake.stage.deep.params deep_profiler/Mmake.deep.params
+            cp "${root}"/Mmake.stage.deep.params \
+                deep_profiler/Mmake.deep.params
         fi
         if test -f "${root}"/Mmake.stage.compiler.params
         then
@@ -1095,12 +1098,14 @@ then
         if test -f "${root}"/Mmake.stage.library.params
         then
             /bin/rm -f library/Mmake.library.params
-            cp "${root}"/Mmake.stage.library.params library/Mmake.library.params
+            cp "${root}"/Mmake.stage.library.params \
+                library/Mmake.library.params
         fi
         if test -f "${root}"/Mmake.stage.runtime.params
         then
             /bin/rm -f runtime/Mmake.runtime.params
-            cp "${root}"/Mmake.stage.runtime.params runtime/Mmake.runtime.params
+            cp "${root}"/Mmake.stage.runtime.params \
+                runtime/Mmake.runtime.params
         fi
         if test -f "${root}"/Mmake.stage.trace.params
         then
@@ -1621,7 +1626,8 @@ EOF
         mkdir deep_profiler
         cd deep_profiler
         ${LN_S} "${root}"/deep_profiler/*.m .
-        cp "${root}"/deep_profiler/Mmake* "${root}"/deep_profiler/Mercury.options .
+        cp "${root}"/deep_profiler/Mmake* \
+            "${root}"/deep_profiler/Mercury.options .
         cp "${root}"/deep_profiler/*_FLAGS.in .
         cp "${root}"/deep_profiler/.mgnu* .
 
@@ -1629,7 +1635,8 @@ EOF
         mkdir mfilterjavac
         cd mfilterjavac
         ${LN_S} "${root}"/mfilterjavac/*.m .
-        cp "${root}"/mfilterjavac/Mmake* "${root}"/mfilterjavac/Mercury.options .
+        cp "${root}"/mfilterjavac/Mmake* \
+            "${root}"/mfilterjavac/Mercury.options .
         cp "${root}"/mfilterjavac/*_FLAGS.in .
         cp "${root}"/mfilterjavac/.mgnu* .
 
@@ -1641,7 +1648,8 @@ EOF
         ${LN_S} "${root}"/install-sh .
         ${LN_S} "${root}"/.*.in .
         rm -f config*.log
-        cp "${root}"/${stage2dir}/Mmake* "${root}"/${stage2dir}/Mercury.options .
+        cp "${root}"/${stage2dir}/Mmake* \
+            "${root}"/${stage2dir}/Mercury.options .
         cd "${root}"
         # set -x
 
@@ -1925,11 +1933,11 @@ EOF
             # files present in the stage 3 directory.
             for file in ${stage3dir}/${dir}/${target_subdir}*.${target_ext}
             do
-                # In the C# and Java grades, some modules have expected differences
-                # between the code generated for them in stage 2 and stage 3,
-                # due to stage 2 being (usually) generated by a 64 bit compiler,
-                # but stage 3 being generated by a compiler in which native
-                # integers are 32 bits.
+                # In the C# and Java grades, some modules have expected
+                # differences between the code generated for them
+                # in stage 2 and stage 3, due to stage 2 being (usually)
+                # generated by a 64 bit compiler, but stage 3 being generated
+                # by a compiler in which native integers are 32 bits.
                 compare_file=true
                 base_file=$(basename "${file}")
                 case "${grade}" in
@@ -2016,7 +2024,8 @@ EOF
                 esac
                 if ${compare_file}
                 then
-                    diff -u "${stage2dir}/${dir}/${target_subdir}${base_file}" \
+                    diff -u \
+                        "${stage2dir}/${dir}/${target_subdir}${base_file}" \
                         "${file}" \
                     || diff_status=1
                 fi
@@ -2360,13 +2369,6 @@ then
             do
                 if test -d "${root}/tests/${testdir}"
                 then
-                    # Temporary addition on 2025 mar 28, intended to
-                    # track down any stray Mercury directories left
-                    # unintentionally by test cases.
-                    echo FIND BAD SUBDIRS
-                    find ${root} -name Mercury
-                    echo END FIND BAD SUBDIRS
-
                     cd "${root}/tests/${testdir}"
                     mmake ${mmake_opts} ${target_opt} ${jfactor} \
                         ${test_grade_opt} ${test_log_opt} \
@@ -2518,7 +2520,8 @@ then
             "${tests_dir}"/EXPECT_FAIL_TESTS
     fi
 
-    sort "${tests_dir}"/EXPECT_FAIL_TESTS > "${tests_dir}"/EXPECT_FAIL_TESTS.sort
+    sort "${tests_dir}"/EXPECT_FAIL_TESTS \
+        > "${tests_dir}"/EXPECT_FAIL_TESTS.sort
     mv "${tests_dir}"/EXPECT_FAIL_TESTS.sort "${tests_dir}"/EXPECT_FAIL_TESTS
 
     sort "${tests_dir}"/FAIL_TESTS > "${tests_dir}"/FAIL_TESTS.sort