Sema: Don't allow CVR qualifiers before structors

We would silently accept volatile ~S() when the user probably intended
to write virtual ~S().

This fixes PR20238.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212555 91177308-0d34-0410-b5e6-96231b3b80d8
Replace a few // comments with /**/ comments in headers, for consistency.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212556 91177308-0d34-0410-b5e6-96231b3b80d8
Don't pull in setjmp.h in -ffreestanding compiles.

Also provide _setjmpex(). r200243 put in _setjmp() and _setjmpex() behind a
comment since jmp_buf wasn't available. r200344 added jmp_buf and put in
_setjmp(), but missed _setjmpex().


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212557 91177308-0d34-0410-b5e6-96231b3b80d8