[Driver] Make "-fno-split-machine-functions" a valid flag for all archs

Previously, clang reports an error when -fno-split-machine-functions
is used for non-X86 archs.

However, in some cases, users may specify flags as
"-fsplit-machine-functions -fother-flags
-fno-split-machine-functions", the first one is from a global flag
set, the last one is used to negate the global flag, we think this is
a valid usage mode.

Another cases is when clang is used to invoke multiple workloads, like
"-x cuda -fsplit-machine-functions -Xarch_device
-fno-split-machine-functions", the latter is used to negate
-fsplit-machine-functions when invoke workloads for GPU."

This change makes this work.

Reviewed By: maskray

Differential Revision: https://reviews.llvm.org/D158755