Support MS inline assembly parsing even on non-X86 target architectures.
See: http://clang-developers.42468.n3.nabble.com/libclang-crash-when-parsing-MS-style-inline-assembly-td4035432.html
The discussion showed that InitializeNativeTarget wasn't exactly necessary and incorrect if we execute on a non-X86 target. Now we explicitly initialize the X86 target info.
Added test to make sure we don't regress.

git-svn-id: http://include-what-you-use.googlecode.com/svn/trunk@493 812d1f90-f944-d88a-411a-122bdc93e1ea