libgfortran LIBGFOR_MINIMAL enhancements.

libgfortran LIBGFOR_MINIMAL enhancements.

Based on GCC trunk r220892, for nvptx-none:

                    === gfortran Summary ===

    # of expected passes            [-31320-]{+32117+}
    # of unexpected failures        [-7222-]{+6821+}
    # of expected failures          78
    # of unresolved testcases       [-6441-]{+6158+}
    # of untested testcases         [-432-]{+391+}
    # of unsupported tests          639

	libgfortran/
	* caf/single.c (caf_runtime_error): Revert 2014-11-28 changes.
	* runtime/minimal.c (STRERR_MAXSZ): Don't define.
	(runtime_error_at, sys_abort): Bring more in line with the
	non-LIBGFOR_MINIMAL code.
	(runtime_warning_at, internal_error): New functions.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@221363 138bc75d-0d04-0410-961f-82ee72b054a4