For CrashRecoveryContext::RunSafelyOnThread, propagate Darwin's PRIO_DARWIN_BG to the new thread if it is
set on the calling thread.

This allows libclang's indexing threads to propagate their priority to the clang module building threads.

rdar://17459872


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211747 91177308-0d34-0410-b5e6-96231b3b80d8
Introduce a string_ostream string builder facilty

string_ostream is a safe and efficient string builder that combines opaque
stack storage with a built-in ostream interface.

small_string_ostream<bytes> additionally permits an explicit stack storage size
other than the default 128 bytes to be provided. Beyond that, storage is
transferred to the heap.

This convenient class can be used in most places an
std::string+raw_string_ostream pair or SmallString<>+raw_svector_ostream pair
would previously have been used, in order to guarantee consistent access
without byte truncation.

The patch also converts much of LLVM to use the new facility. These changes
include several probable bug fixes for truncated output, a programming error
that's no longer possible with the new interface.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211749 91177308-0d34-0410-b5e6-96231b3b80d8
[X86] AVX512: Fix asm syntax for packed vcmp

The *_alt defs for vcmp are used by the InstParser (the asm string in the main
def is used by the InstPrinter) .  The former was accepting vector registers
as destination rather than mask registers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211750 91177308-0d34-0410-b5e6-96231b3b80d8
MSVC build fix following r211749

Avoid strndup()

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211752 91177308-0d34-0410-b5e6-96231b3b80d8
Don't build switch tables for dllimport and TLS variables in GEPs

This is a follow-up to r211331, which failed to notice that we were
returning early from ValidLookupTableConstant for GEPs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211753 91177308-0d34-0410-b5e6-96231b3b80d8