Avoid evaluating Neon macro arguments more than once by disabling type checks.

Avoid evaluating Neon macro arguments more than once by disabling type checks.
It turns out that the use of "__extension__" in these macros was disabling
the expected "incompatible pointer" warnings, so these type checks were not
doing anything anyway.  They introduced a serious bug by evaluating some
macro arguments twice, which is a big problem for arguments with side effects.
I'll have to find another way to get the right type checking.  Radar 9947657.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137680 91177308-0d34-0410-b5e6-96231b3b80d8