As per #142559, this marks ftrunc as legal for Neon and upgrades the existing
arm.neon.vrintz intrinsics.

This reverts commit cd826d6e840ed33ad88458c862da5f9fcc6e908c and relands
27c1aa9b9cf9e0b14211758ff8f7d3aaba24ffcf
This fixes #104765

I tweaked the code to avoid an OOB.

Adds support for __sys Clang builtin for AArch64

__sys is a long existing MSVC intrinsic used to manage caches, tlbs, etc
by writing to system registers:
* It takes a macro-generated constant and uses it to form the AArch64 SYS instruction which is MSR with op0=1. The macro drops op0 and expects the implementation to hardcode it to 1 in the encoding.
* Volume use is in systems code (kernels, hypervisors, boot environments, firmware)
* Has an unused return value due to MSVC cut/paste error

Implementation:
* Clang builtin, sharing code with Read/WriteStatusReg
* Hardcodes the op0=1
* Explicitly returns 0
* Code-format change from clang-format
* Unittests included
* Not limited to MSVC-environment as its generally useful and neutral

In Vulkan, the signedness of the accesses to images has to match the
signedness of the backing image.
    
See

https://docs.vulkan.org/spec/latest/chapters/textures.html#textures-input,
where it says the behaviour is undefined if
    
> the signedness of any read or sample operation does not match the
signedness of the image’s format.
    
Users who define say an `RWBuffer<int>` will create a Vulkan image with
a signed integer format. So the HLSL that is generated must match that
expecation.
    
The solution we use is to generate a `spirv.SignedImage` target type for
signed integer instead of `spirv.Image`. The two types are otherwise the
same.
    
The backend will add the `signExtend` image operand to access to the
image to ensure the image is access as a signed image.
    
Fixes #144580

In a previous commit, the llvm-config-defined macro
LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING was renamed to
LLVM_ENABLE_DEBUGLOC_TRACKING_COVERAGE. One instance of this in Clang
remains unchanged; this patch renames it, and adds an explicit
llvm-config inclusion to ensure the define doesn't silently get removed.

NFC outside of coverage tracking builds, which we do not currently test.

As per #142559, this marks fceil as legal for Neon and upgrades the existing
arm.neon.vrintp intrinsics.

Both of these functions return void.

Verify that the alignments specified by clang TargetInfo match the
alignments specified by LLVM data layout, which will hopefully prevent
accidental mismatches in the future.

This currently contains opt-outs for a number of of existing mismatches.

I'm also skipping the verification if options like `-malign-double` are
used, or a language that mandates sizes/alignments that differ from C.

The verification happens in CodeGen, as we can't have an IR dependency
in Basic.

E is already of Expr * and shares the same declaration among all these
cases.

As per #142559, this marks fround as legal for Neon and upgrades the existing
arm.neon.vrinta intrinsics.