Part of ongoing work to make core ORC operations asynchronous.

This only affects the runner utilities, not the AllocationActions themselves.
The AllocationActions will be made asynchronous in a future patch.

This PR will solve the issue with leaking shared memory we have after running llvm lit test on z/OS.
In particular llvm/unittests/ExecutionEngine/Orc/SharedMemoryMapperTest.cpp was causing the leak.

Identified with misc-include-cleaner.

Without these explicit includes, removing other headers, who implicitly
include llvm-config.h, may have non-trivial side effects.

Fix 'use of undeclared identifier' build errors for shm_ functions on
z/OS by implementing the functionality using shmget(), shmat(), and
shmdt(). Use the BLAKE3 hash to map the name of the shared memory to a
key.

---------

Co-authored-by: Kai Nacke <kai.peter.nacke@ibm.com>

LLVM is inconsistent about how it converts `errno` to `std::error_code`.
This can cause problems because values outside of `std::errc` compare
differently if one is system and one is generic on POSIX systems.

This is even more of a problem on Windows where use of the system
category is just wrong, as that is for Windows errors, which have a
completely different mapping than POSIX/generic errors. This patch fixes
one instance of this mistake in `JSONTransport.cpp`.

This patch adds `errnoAsErrorCode()` which makes it so people do not
need to think about this issue in the future. It also cleans up a lot of
usage of `errno` in LLVM and Clang.

The *Policy suffix came from the earlier MemAllocPolicy type, where it was
included to distinguish the type from a memory-allocation operation.
MemLifetime is a noun already, so the *Policy suffix is just dead weight now.

This reapplies 2cc64df0bd6a802eab592dbc282463c3e4a4281c, which was reverted in
5379c46d490640bfa80283e00240b6f1006092b4 due to bot failures.

The new patch contains fixes to ELFLinkGraphBuilder.h to better handle
non-SHT_ALLOC sections (these were being accidentally skipped in the previous
patch), and to skip SHT_NULL sections.

This reverts commit 2cc64df0bd6a802eab592dbc282463c3e4a4281c while I investigate
bot failures (e.g. https://lab.llvm.org/buildbot/#/builders/3/builds/23081).