Update the intel intrinsic headers to use the target attribute support.

This involved removing the conditional inclusion and replacing them
with target attributes matching the original conditional inclusion
and checks. The testcase update removes the macro checks for each
file and replaces them with usage of the __target__ attribute, e.g.:

int __attribute__((__target__(("sse3")))) foo(int a) {
  _mm_mwait(0, 0);
  return 4;
}

This usage does require the enclosing function have the requisite
__target__ attribute for inlining and code generation - also for
any macro intrinsic uses in the enclosing function. There's no change
for existing uses of the intrinsic headers.

llvm-svn: 239883