Fix typo in patch to fix clang build.
Adjust the set of headers installed with clang to match llvm90. Also
correct the location of the patch.
Reported by: yuri (lack on unwind.h)
Update to a new version (LLVM HEAD is now 9.0.0).
Remove clang headers conflicting with FreeBSD headers. I'd throught
this was nolonger required, but it seems to still be necessicary in at
least some cases.
Submitted by: Alfredo Dal'Ava Junior
Differential Revision: https://reviews.freebsd.org/D18879