The ICE in PR preprocessor/78569 appears to be due to an attempt to
generate substring locations in a .i file where the underlying .c file
has changed since the .i file was generated.

This can't work, so it seems safest for the on-demand substring
locations to be unavailable for such files, falling back to
"whole string" locations for such cases.

gcc/ChangeLog:
	PR preprocessor/78569
	* input.c (get_substring_ranges_for_loc): Fail gracefully if
	line directives were present.

gcc/testsuite/ChangeLog:
	PR preprocessor/78569
	* gcc.dg/format/pr78569.c: New test case.

From-SVN: r242990