Refactored some rules in Make-lang.in and portfix calcpath.

Refactored some rules in Make-lang.in and portfix calcpath.

Removed the -e option to realpath in the calcpath tool so
that gm2 builds on FreeBSD.  Also refactored some of the
rules in Make-lang.in and added and tidied up some of the
comments.

gcc/m2/ChangeLog:

	* m2/Make-lang.in (GCC_HEADER_DEPENDENCIES_FOR_M2): New define.
	m2/gm2-gcc/%.o: Add GCC_HEADER_DEPENDENCIES_FOR_M2 as a dependent.
	m2/gm2-lang.o: Add GCC_HEADER_DEPENDENCIES_FOR_M2 as a dependent.
	m2/stor-layout.o: Add GCC_HEADER_DEPENDENCIES_FOR_M2 as a
	dependent.
	m2/m2pp.o: Add GCC_HEADER_DEPENDENCIES_FOR_M2 as a
	dependent.
	m2/gm2-gcc/rtegraph.o: Add GCC_HEADER_DEPENDENCIES_FOR_M2 as a
	dependent.
	c-family/m2pp.o: Add GCC_HEADER_DEPENDENCIES_FOR_M2 as a
	dependent.  Added new comments.
	* m2/tools-src/calcpath: Remove -e option to realpath
	to help the build on FreeBSD.

Signed-off-by: Gaius Mulley <gaius.mulley@southwales.ac.uk>