Support building musl for arm and arm64

Move the -frounding-math argument to only apply to x86 and x86_64,
it is unsupported on arm and arm64.

Pass -Wno-ignored-pragmas on arm and arm64, they don't support
the #pragma STDC FENV_ACCESS ON.

Bug: 236052820
Test: musl sysroots build for arm and arm64
Change-Id: Ia9fddc4bd70fb2c4bd7e57dc21ef762220cd6db8
1 file changed