re PR preprocessor/15638 (gcc should have option to treat missing headers as fatal)

	PR preprocessor/15638
gcc:
	* c-common.c (c_cpp_error): Handle CPP_DL_FATAL.

gcc/fortran:
	* cpp.c (cb_cpp_error): Handle CPP_DL_FATAL.

gcc/testsuite:
	* gcc.dg/cpp/missing-header-1.c: New test.
	* gcc.dg/cpp/include2.c: Only test #include <>.  Expect
	"compilation terminated" message.
	* gcc.dg/cpp/include2a.c: New test.  Copy of include2.c but only
	test #include "".
	* gcc.dg/pch/counter-2.c, gcc.dg/pch/valid-1.c,
	gcc.dg/pch/valid-2.c, gcc.dg/pch/warn-1.c: Expect "compilation
	terminated" message.

libcpp:
	* files.c (_cpp_find_file): Call open_file_failed after diagnosing
	invalid PCH.
	(open_file_failed): Make error for missing file fatal.
	* include/cpplib.h (CPP_DL_FATAL): Define.

From-SVN: r145341