clang does not require -msse2 or -msse for inline, except
the "x" parameter.  So change this to "m" for 32 bit.  64 bit
requires sse2 so use "x" for 64 bit.

gcc requires -msse for xmm registers in clobber list.
Reduce compiler requirement from -msse2 to -msse for enabling
assembly.

Bug: libyuv:754, libyuv:757
Test: CC=clang CXX=clang++ CFLAGS="-m32" CXXFLAGS="-m32 -mno-sse -O2" make -f linux.mk
Change-Id: I86df72cfee80b7d349561c1fd7c97ad360767255
Reviewed-on: https://chromium-review.googlesource.com/759303Reviewed-by: richard winterton <rrwinterton@gmail.com>
Reviewed-by: Frank Barchard <fbarchard@google.com>
Commit-Queue: Frank Barchard <fbarchard@google.com>