Use sub-modules to structure the modules in the Mercury compiler directory.

The main aim of this change is to make the overall, high-level structure
of the compiler clearer, and to encourage better encapsulation of the
major components.

compiler/libs.m:
compiler/backend_libs.m:
compiler/parse_tree.m:
compiler/hlds.m:
compiler/check_hlds.m:
compiler/transform_hlds.m:
compiler/bytecode_backend.m:
compiler/aditi_backend.m:
compiler/ml_backend.m:
compiler/ll_backend.m:
compiler/top_level.m:
	New files.  One module for each of the major components of the
	Mercury compiler.  These modules contain (as separate sub-modules)
	all the other modules in the Mercury compiler, except gcc.m and
	mlds_to_gcc.m.

Mmakefile:
compiler/Mmakefile:
	Handle the fact that the top-level module is now `top_level',
	not `mercury_compile' (since `mercury_compile' is a sub-module
	of `top_level').

compiler/Mmakefile:
	Update settings of *FLAGS-<modulename> to use the appropriate
	nested module names.

compiler/recompilation_check.m:
compiler/recompilation_version.m:
compiler/recompilation_usage.m:
compiler/recompilation.check.m:
compiler/recompilation.version.m:
compiler/recompilation.version.m:
	Convert the `recompilation_*' modules into sub-modules of the
	`recompilation' module.

compiler/*.m:
compiler/*.pp:
	Module-qualify the module names in `:- module', `:- import_module',
	and `:- use_module' declarations.

compiler/base_type_info.m:
compiler/base_type_layout.m:
	Deleted these unused empty modules.

compiler/prog_data.m:
compiler/globals.m:
	Move the `foreign_language' type from prog_data to globals.

compiler/mlds.m:
compiler/ml_util.m:
compiler/mlds_to_il.m:
	Import `globals', for `foreign_language'.

Mmake.common.in:
trace/Mmakefile:
runtime/Mmakefile:
	Rename the %.check.c targets as %.check_hdr.c,
	to avoid conflicts with compiler/recompilation.check.c.

Mmakefile

@@ -68,9 +68,9 @@ browser/$(deps_subdir)mdb.dep:
 	+cd browser && $(SUBDIR_MMAKE) depend
 
 .PHONY: dep_compiler
-dep_compiler: compiler/$(deps_subdir)mercury_compile.dep
+dep_compiler: compiler/$(deps_subdir)top_level.dep
 
-compiler/$(deps_subdir)mercury_compile.dep: library/$(deps_subdir)library.dep
+compiler/$(deps_subdir)top_level.dep: library/$(deps_subdir)library.dep
 	+cd compiler && $(SUBDIR_MMAKE) depend
 
 .PHONY: dep_profiler
@@ -80,8 +80,12 @@ profiler/$(deps_subdir)mercury_profile.dep: library/$(deps_subdir)library.dep
 	+cd profiler && $(SUBDIR_MMAKE) depend
 
 .PHONY: dep_deep_profiler
+ifeq ("$(ENABLE_DEEP_PROFILER)","yes")
 dep_deep_profiler: deep_profiler/$(deps_subdir)mdprof_cgi.dep \
 		deep_profiler/$(deps_subdir)mdprof_server.dep
+else
+dep_deep_profiler:
+endif
 
 deep_profiler/$(deps_subdir)mdprof_cgi.dep: library/$(deps_subdir)library.dep
 	+cd deep_profiler && $(SUBDIR_MMAKE) mdprof_cgi.depend