[CMake] CHECK_C_COMPILER_FLAG (very) broken with icc!

[Szilárd Páll]

Hi,

I'm using the Intel Compiler v12 and to have a robust build generator,
before adding flags to CFLAGS I test them.

The following buggy behavior exists in CMake up to v2.8.7:

- As Intel issues
"icc: command line warning #10006: ignoring unknown option '-asdf'"
type warnings which are not handled in CHECK_C_COMPILER_FLAG, checking
CFLAGS is completely broken (also reported in bugreport #12576).

- However, checking for "-openmp" still returns false!

Any idea why does this happen? I can write a custom
CHECK_C_COMPILER_FLAG which includes a check for the icc, but I've no
clue why the "-openmp" check doesn't work.

Additionally, IMHO it's quite unfortunate that such a widely used
compiler as the Intel Compiler has such flaky support in CMake. I
would rather like to see a more limited feature set, but a well tested
and robust one.

Cheers,
--
Szilárd