249e905

[SaferCPP] analyze-safer-cpp reports "OK" for files that fail to compile

https://bugs.webkit.org/show_bug.cgi?id=317931
rdar://181330433

Reviewed by NOBODY (OOPS!).

analyze-safer-cpp ignored clang's exit code, and its diagnostic regex matches
"error:" but not "fatal error:", so a file that failed to compile was reported
as "OK" with a zero exit. On a configured-but-unbuilt compile_commands tree
(missing generated headers) every file "passes" without being analyzed.

Surface a non-zero clang exit with no parsed diagnostic as an error, printing
the file and clang's output, so a compile failure fails the run instead of
passing silently.

249e905

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