This will make it possible for tablegen to make subtarget
dependent decisions without adding new arguments to every
target.

---------

Co-authored-by: Sergei Barannikov <barannikov88@gmail.com>

Not all SPIR-V extensions are allows in every environment. When we use
the `-spirv-ext=all` option, the backend currently believes that all
extensions can be used.

This commit filters out the extensions on the command line to remove
those that are not known to be allowed for the current environment.

Alternatives considered: I considered modifying the
SPIRVExtensionsParser::parse to use a different list of extensions for
"all" depending on the target triple. However that does not work because
the target triple is not available, and cannot be made available in a
reasonable way.

Fixes #147717

---------

Co-authored-by: Victor Lomuller <victor@codeplay.com>

A new test added for spirv-friendly builtins for
SPV_KHR_bit_instructions unveiled that current mechanism to detect
whether SPIRV Backend is in OpenCL environment or Vulkan environment was
not good enough. This PR updates how to detect the environment and all
the tests accordingly.

*UPDATE*: the new approach is having a new member in `SPIRVSubtarget` to
represent the environment. It can be either OpenCL, Kernel or Unknown.
If the triple is explicit, we can directly set it at the creation of the
`SPIRVSubtarget`, otherwise we just leave it unknown until we find other
information that can help us set the environment. For now, the only
other information we use to set the environment is `hlsl.shader`
attribute at `SPIRV::ExecutionModel::ExecutionModel
getExecutionModel(const SPIRVSubtarget &STI, const Function &F)`. Going
forward we should consider also specific instructions that are
Kernel-exclusive or Shader-exclusive.

---------

Co-authored-by: marcos.maronas <mmaronas@smtp.igk.intel.com>

These are identified by misc-include-cleaner.  I've filtered out those
that break builds.  Also, I'm staying away from llvm-config.h,
config.h, and Compiler.h, which likely cause platform- or
compiler-specific build failures.

DenseSet, SmallPtrSet, SmallSet, SetVector, and StringSet recently
gained C++23-style insert_range.  This patch replaces:

  Dest.insert(Src.begin(), Src.end());

with:

  Dest.insert_range(Src);

This patch does not touch custom begin like succ_begin for now.

This PR fixes https://github.com/llvm/llvm-project/issues/124703:
* added a new API call `SPIRVTranslate` that is to replace entirely old
`SPIRVTranslateModule` after existing clients switch into the new
function;
* the new `SPIRVTranslate` doesn't require option parsing, replacing the
`Opts` argument with explicit `CodeGenOptLevel` and `Triple` arguments;
* the old `SPIRVTranslateModule` call is a wrapper for `SPIRVTranslate`,
it doesn't require option parsing either and doesn't hold any logic
inside except for converting string options into `CodeGenOptLevel` and
`Triple` arguments;
* usage of the extensions list is reworked to avoid writes to the global
cl::opt variable `lib/Target/SPIRV/SPIRVSubtarget.cpp::Extensions` --
instead a new class member in SPIRVSubtarget.cpp is implemented that
allows to replace supported extensions after SPIRVSubtarget.cpp is
created;
* both API calls don't require option parsing and don't write to global
cl::opt variables.

Other related/required changes:
* SPIRV::Capability::Shader is marked as an capability of lesser
priority for OpenCL environment (to remediate absence of the
"avoid-spirv-capabilities" command line option in API calls);
* unit tests are updated and extended to cover testing of a newer API
call;
* old API call is marked with TODO to remove it after existing clients
switch into the new function.

Before this change InstrSet in SPIRVEmitIntrinsics was uninitialized
before running runOnFunction. This change adds a new function
getPreferredInstructionSet in SPIRVSubtarget.

- create a clang built-in in Builtins.td
- link dot4add_i8packed in hlsl_intrinsics.h
- add lowering to spirv backend through expansion of operation as OPSDot
is missing up to SPIRV 1.6 in SPIRVInstructionSelector.cpp
- add lowering to spirv backend using OpSDot in applicable SPIRV version
or if SPV_KHR_integer_dot_product is enabled
- add dot4add_i8packed intrinsic to IntrinsicsDirectX.td and mapping to
DXIL.td op Dot4AddI8Packed

- add tests for HLSL intrinsic lowering to dx/spv intrinsic in
dot4add_i8packed.hlsl
- add tests for sema checks in dot4add_i8packed-errors.hlsl
- add test of spir-v lowering in SPIRV/dot4add_i8packed.ll
- add test to dxil lowering in DirectX/dot4add_i8packed.ll
    
 Resolves #99220

The goal of this PR is to facilitate integration of SPIRV Backend into
misc 3rd party tools and libraries by means of exposing an API call that
translate LLVM module to SPIR-V and write results into a string as
binary SPIR-V output, providing diagnostics on fail and means of
configuring translation in a style of command line options.

An example of a use case may be Khronos Translator that provides
bidirectional translation LLVM IR <=> SPIR-V, where LLVM IR => SPIR-V
step may be substituted by the call to SPIR-V Backend API, implemented
by this PR.