BUG: Don't enable SSE rounding with OSX and gccxml

As of patch 409d86407e762c71eae598e7f8ed007b0e0a7ded, the required
intrinsic header is no longer included with during GCC_XML
running. The SSE2 intrinsic can safely be disabled during GCC_XML
parsing.

Change-Id: I7c7336f81753257b61dc631f5197af27b6ac6905
Merge topic 'FixOSXGCCXMLSSEInstructions'

f0f96dfc BUG: Don't enable SSE rounding with OSX and gccxml