config/debuginfod.m4: Use PKG_CHECK_MODULES

Use PKG_CHECK_MODULES to set debuginfod autoconf vars. Also add
pkg.m4 to config/.

ChangeLog:

	* config/debuginfod.m4: use PKG_CHECK_MODULES.
	* config/pkg.m4: New file.
	* configure: Rebuild.
	* configure.ac: Remove AC_DEBUGINFOD.

ChangeLog/binutils:

	* Makefile.am: Replace LIBDEBUGINFOD with DEBUGINFOD_LIBS.
	* Makefile.in: Rebuild.
	* configure: Rebuild.
	* doc/Makefile.in: Rebuild.

ChangeLog/gdb:

	* Makefile.in: Replace LIBDEBUGINFOD with DEBUGINFOD_LIBS.
	* configure: Rebuild.