sphinx: add --with-sphinx-build

sphinx: add --with-sphinx-build

gcc/ChangeLog:

	* Makefile.in: Support --with-sphinx-build.
	* configure.ac:
	* configure: Regenerate.

gcc/ada/ChangeLog:

	* gcc-interface/Make-lang.in: Support --with-sphinx-build.

gcc/d/ChangeLog:

	* Make-lang.in: Support --with-sphinx-build.

gcc/fortran/ChangeLog:

	* Make-lang.in: Support --with-sphinx-build.

gcc/go/ChangeLog:

	* Make-lang.in: Support --with-sphinx-build.

gcc/jit/ChangeLog:

	* Make-lang.in: Support --with-sphinx-build.

libgomp/ChangeLog:

	* Makefile.in: Support --with-sphinx-build.
	* configure.ac: Likewise..
	* configure: Regenerate.

libiberty/ChangeLog:

	* Makefile.in: Support --with-sphinx-build.
	* configure.ac: Likewise.
	* configure: Regenerate.

libitm/ChangeLog:

	* Makefile.in: Support --with-sphinx-build.
	* configure.ac: Likewise.
	* configure: Regenerate.

libquadmath/ChangeLog:

	* Makefile.in: Support --with-sphinx-build.
	* configure.ac: Likewise.
	* configure: Regenerate.