BSD format-extensions break the gcc testsuite

[Pedro F. Giffuni]

Hello;

I have been trying to build kernels with llvm-gcc4 so
I took the code to add -fformat-extensions from our
system gcc and I added it to llvm-gcc4.

Unfortunately, even when format-extensions are not
set, it seems to alter gcc's behaviour.

The llvm committer reported this issue:
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...

I applied the three patches in PR9097, and ran the LLVM test suite and the GCC test suite.  The news is generally positive, but this test case:

    .../llvmgcc42.test/gcc/testsuite/gcc.dg/format/attr-3.c

now segfaults on this declaration:

    extern void fe0 (const char *, ...) __attribute__((format(12345, 1, 2)));

Both the patched and unpatched compiler generate lots of diagnostics for this test case, but the unpatched compiler doesn't segfault.
...
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Anyone that can help? I suspect this issue may also be causing trouble in our base compiler.

cheers,

Pedro.