Changes

[libcxx] Port to OpenBSD

Add initial OpenBSD support.

Reviewed By: ldionne

Differential Revision: https://reviews.llvm.org/D94205

[InstSimplify] Don't fold gep p, -p to null

This is a partial fix for https://bugs.llvm.org/show_bug.cgi?id=44403.
Folding gep p, q-p to q is only legal if p and q have the same
provenance. This fold should probably be guarded by something like
getUnderlyingObject(p) == getUnderlyingObject(q).

This patch is a partial fix that removes the special handling for
gep p, 0-p, which will fold to a null pointer, which would certainly
not pass an underlying object check (unless p is also null, in which
case this would fold trivially anyway). Folding to a null pointer
is particularly problematic due to the special handling it receives
in many places, making end-to-end miscompiles more likely.

Differential Revision: https://reviews.llvm.org/D93820

[OpenMP] Fixed include directories for OpenMP when building OpenMP with LLVM_ENABLE_RUNTIMES

Some LLVM headers are generated by CMake. Before the installation,
LLVM's headers are distributed everywhere, some of which are in
`${LLVM_SRC_ROOT}/llvm/include/llvm`, and some are in
`${LLVM_BINARY_ROOT}/include/llvm`. After intallation, they're all in
`${LLVM_INSTALLATION_ROOT}/include/llvm`.

OpenMP now depends on LLVM headers. Some headers depend on headers generated
by CMake. When building OpenMP along with LLVM, a.k.a via `LLVM_ENABLE_RUNTIMES`,
we need to tell OpenMP where it can find those headers, especially those still
have not been copied/installed.

Reviewed By: jdoerfert, jhuber6

Differential Revision: https://reviews.llvm.org/D94534

[libomptarget][amdgpu][nfc] Fix build on centos

[libomptarget][amdgpu][nfc] Fix build on centos

rtl.cpp replaced 224 with a #define from elf.h, but that
doesn't work on a centos 7 build machine with an old elf.h

Reviewed By: ronlieb

Differential Revision: https://reviews.llvm.org/D94528

[clang][aarch64] Precondition isHomogeneousAggregate on isCXX14Aggregate

MSVC on WoA64 includes isCXX14Aggregate in its definition. This is de-facto
specification on that platform, so match msvc's behaviour.

Fixes: https://bugs.llvm.org/show_bug.cgi?id=47611

Co-authored-by: Peter Waller <peter.waller@arm.com>

Differential Revision: https://reviews.llvm.org/D92751