mpl: Improved check for AVX/AVX512F support

[raffenet]

Pull Request Description

PAC_C_CHECK_COMPILER_OPTION checks for warning messages, but those can
be silenced by the user e.g. with clang's -Qunused-arguments. Try to
compile a simple program using the extensions needed by MPL for a more
robust test for this functionality.

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[raffenet]

test:mpich/ch4/most
test:mpich/ch3/most

[raffenet]

This does resolve the issue, but perhaps the compiler warning check for -mavx is the wrong approach and we should just compile test a simple avx and avx512f program. What do you think @hzhou?

[hzhou]

This does resolve the issue, but perhaps the compiler warning check for -mavx is the wrong approach and we should just compile test a simple avx and avx512f program. What do you think @hzhou?

I agree

[raffenet]

test:mpich/ch4/most
test:mpich/ch3/most

[hzhou]

Looks good to me