`CounterPair` can hold `<uint32_t, uint32_t>` instead of current
`unsigned`, to hold also the counter number of SkipPath. For now, this
change provides the skeleton and only `CounterPair::Executed` is used.

Each counter number can have `None` to suppress emitting counter
increment. 2nd element `Skipped` is initialized as `None` by default,
since most `Stmt*` don't have a pair of counters.

This change also provides stubs for the verifier. I'll provide the impl
of verifier for `+Asserts` later.

`markStmtAsUsed(bool, Stmt*)` may be used to inform that other side
counter may not emitted.

`markStmtMaybeUsed(S)` may be used for the `Stmt` and its inner will be
excluded for emission in the case of skipping by constant folding. I put
it into places where I found.

`verifyCounterMap()` will check the coverage map and the counter map,
and can be used to report inconsistency.

These verifier methods shall be eliminated in `-Asserts`.


https://discourse.llvm.org/t/rfc-integrating-singlebytecoverage-with-branch-coverage/82492

This executable construct has a larger list of clauses than some of the
others, plus has some additional restrictions.  This patch implements
the AST node, plus the 'cannot be the body of a if, while, do, switch,
    or label' statement restriction.  Future patches will handle the
    rest of the restrictions, which are based on clauses.

The 'set' construct is another fairly simple one, it doesn't have an
associated statement and only a handful of allowed clauses. This patch
implements it and all the rules for it, allowing 3 of its for clauses.
The only exception is default_async, which will be implemented in a
future patch, because it isn't just being enabled, it needs a complete
new implementation.

- adding Flatten and Branch to if stmt.
- adding dxil control flow hint metadata generation
- modifing spirv OpSelectMerge to account for the specific attributes.

Closes #70112

---------

Co-authored-by: Joao Saffran <jderezende@microsoft.com>
Co-authored-by: joaosaffran <joao.saffran@microsoft.com>

- Update pr labeler so new SPIRV files get properly labeled.
- Add distance target builtin to BuiltinsSPIRV.td.
- Update TargetBuiltins.h to account for spirv builtins.
- Update clang basic CMakeLists.txt to build spirv builtin tablegen.
- Hook up sema for SPIRV in Sema.h|cpp, SemaSPIRV.h|cpp, and
SemaChecking.cpp.
- Hookup sprv target builtins to SPIR.h|SPIR.cpp target.
- Update GBuiltin.cpp to emit spirv intrinsics when we get the expected
spirv target builtin.

Consensus was reach in this RFC to add both target builtins and pattern
matching:
https://discourse.llvm.org/t/rfc-add-targetbuiltins-for-spirv-to-support-hlsl/83329.

pattern matching will come in a separate pr this one just sets up the
groundwork to do target builtins for spirv.

partially resolves
[#99107](https://github.com/llvm/llvm-project/issues/99107)

Conflicts:
	clang/lib/CodeGen/CodeGenPGO.cpp
	clang/lib/CodeGen/CoverageMappingGen.cpp