The intended purpose of the option is both for targets that don't
support phobos yet, and for gdc itself to support bootstrapping itself
as a self-hosted D compiler.
The libphobos testsuite has been updated to only add libphobos to the
search paths if it's being built. A new D2 testsuite directive
RUNNABLE_PHOBOS_TEST has also been patched in to disable some runnable
tests that have phobos dependencies, of which is a temporary measure
until upstream DMD fixes or removes these tests entirely.
gcc/testsuite/ChangeLog:
* lib/gdc-utils.exp (gdc-convert-test): Add dg-skip-if for tests that
depending on the phobos standard library.
libphobos/ChangeLog:
* configure: Regenerate.
* configure.ac: Add --with-libphobos-druntime-only option and the
conditional ENABLE_LIBDRUNTIME_ONLY.
* configure.tgt: Define LIBDRUNTIME_ONLY.
* src/Makefile.am: Add phobos sources if not ENABLE_LIBDRUNTIME_ONLY.
* src/Makefile.in: Regenerate.
* testsuite/testsuite_flags.in: Add phobos path if compiling phobos.
