gcc/ChangeLog:
* configure.ac (gcc_version): Expose this value for use via
AC_SUBST, since the jit code needs it within the new file
libgccjit.pc.in.
(doc_build_sys): New variable, set to "sphinx" if
sphinx is installed, falling back to "texinfo" otherwise.
(gcc-driver-name.h): Generate a gcc-driver-name.h file containing
GCC_DRIVER_NAME for the benefit of jit/jit-playback.c.
* configure: Regenerate.
* Makefile.in (doc_build_sys): New.
(bindir): New.
(pkgconfigdir): New.
(installdirs): Add creation of $(DESTDIR)$(pkgconfigdir).
(site.exp): When constructing site.exp, add a line to set "bindir".