mpich: Use gcc runtime with clang for x86/x86_64
mpich: Use gcc runtime with clang for x86/x86_64

It needs symbols like __multf3 which are not in compiler-rt

Signed-off-by: Khem Raj <729d64b6f67515e258459a5f6d20ec88b2caf8df@gmail.com>

kraj/meta-clang,kraj/meta-clang,kraj/meta-clang