sphinx: support Sphinx in build system

config/ChangeLog:

	* acx.m4: Do not wrap REPORT_BUGS_TO.

ChangeLog:

	* configure: Regenerate.
	* configure.ac: Support Sphinx based documentation.

gcc/ChangeLog:

	* Makefile.in: Support Sphinx based documentation.
	* configure: Regenerate.
	* configure.ac: Support Sphinx based documentation.
	* genhooks.cc (struct s_hook): Emit tm.rst.in file.

gcc/cp/ChangeLog:

	* Make-lang.in: Support Sphinx based documentation.

gcc/d/ChangeLog:

	* Make-lang.in: Support Sphinx based documentation.

gcc/fortran/ChangeLog:

	* Make-lang.in: Support Sphinx based documentation.

gcc/go/ChangeLog:

	* Make-lang.in: Support Sphinx based documentation.

libgomp/ChangeLog:

	* Makefile.in: Support Sphinx based documentation.

libiberty/ChangeLog:

	* Makefile.in: Support Sphinx based documentation.

libitm/ChangeLog:

	* Makefile.in: Support Sphinx based documentation.

libquadmath/ChangeLog:

	* Makefile.in: Support Sphinx based documentation.