Install the Bohem GC headers with non-C grade compilers.

Ensure that the header files for the Boehm GC are installed when the compiler
is built in a non-C grade.  They need to be installed in case installation
includes a (.gc) C grade.

Mmakefile:
    Make the install_boehm target install the GC headers in non-C grades.

    Fix a typo.

Mmakefile

@@ -239,7 +239,7 @@ depend_mfilterjavac:
 
 # NOTE: there are two targets that concern the util directory here.  The first
 # is the "util_no_rt" target (short for "util no runtime") and the second is the
-# "util" target.  The first target builds thaose programs in the util directory
+# "util" target.  The first target builds those programs in the util directory
 # that do *not* depend on the runtime directory, at present just mfiltercc.
 # The second target builds the rest.  Things are arranged in this fashion so
 # that when building the source distribution we can build mfiltercc before
@@ -585,10 +585,19 @@ install_runtime: runtime
 install_trace: trace
 	+cd trace && $(SUBDIR_MMAKE) install
 
+# When building the compiler in a non-C grade the header files for the Boehm GC
+# still need to be installed, otherwise an installed non-C grade compiler won't
+# be able to compile anything in .gc grades.
+#
 .PHONY: install_boehm_gc
+ifeq ("$(filter csharp% java% erlang%,$(GRADE))","")
 install_boehm_gc: boehm_gc
 	+gc_grade=`scripts/ml --grade $(GRADE) --print-gc-grade`; \
 	cd boehm_gc && $(SUBDIR_MMAKE) install GC_GRADE=$$gc_grade
+else
+install_boehm_gc: boehm_gc
+	cd boehm_gc && $(SUBDIR_MMAKE) install_headers GC_GRADE=gc
+endif
 
 .PHONY: install_library
 install_library: dep_library library