libphobos: Organize druntime and phobos tests under common directory

The druntime and druntime_shared tests are identical, save for one
compiled with `-static-libphobos' and the other `-shared-libphobos'.
Move them to libphobos.druntime/static and libphobos.druntime/shared
respectively.  This has also been done for libphobos.phobos.

libphobos/ChangeLog:

	* testsuite/libphobos.druntime_shared/druntime_shared.exp: Move to...
	* testsuite/libphobos.druntime/shared/druntime-shared.exp: ...here.
	* testsuite/libphobos.druntime/druntime.exp: Move to...
	* testsuite/libphobos.druntime/static/druntime-static.exp: ...here.
	* testsuite/libphobos.phobos_shared/phobos_shared.exp: Move to...
	* testsuite/libphobos.phobos/shared/phobos-shared.exp: ...here.
	* testsuite/libphobos.phobos/phobos.exp: Move to...
	* testsuite/libphobos.phobos/static/phobos-static.exp: ...here.