As a prerequesite for PR94304, it becomes easier to manage selectively
compiling sublibraries when there's only one library to link to.

So a druntime convenience library is built to be part of phobos, however
separate druntime library is still built and installed, to allow linking
only to the core runtime explicitly, rather than pulling in the entire
standard library with it.

The gdc driver no longer generates an '-lgdruntime' option, and the
inclusion of the libdruntime library path has been removed from the
testsuite.

gcc/d/ChangeLog:

	* d-spec.cc (LIBDRUNTIME): Remove.
	(LIBDRUNTIME_PROFILE): Remove.
	(lang_specific_driver): Don't link in libgdruntime.

gcc/testsuite/ChangeLog:

	* lib/gdc.exp (gdc_link_flags): Remove libdruntime library path.

libphobos/ChangeLog:

	* d_rules.am (libdgruntime_la_LINK): Move to libdruntime/Makefile.am.
	(libgphobos_la_LINK): Move to src/Makefile.am
	* libdruntime/Makefile.am: Add libgdruntime_convenience library.
	* libdruntime/Makefile.in: Regenerate.
	* src/Makefile.am (libgphobos_la_LIBADD): Add libgdruntime_convenience
	library.
	(libgphobos_la_DEPENDENCIES): Likewise.
	* src/Makefile.in: Regenerate.
	* testsuite/lib/libphobos.exp: Remove libdruntime library paths.
	* testsuite/testsuite_flags.in: Likewise.