Factor out code in `populateCounters()` and `populateCoverage()` used to
grab the record into `PGOUseFunc::getRecord()` to reduce code
duplication. And return `NamedInstrProfRecord` in `getInstrProfRecord()`
to avoid an unnecessary cast. No functional change is intented.

The InstrProf headers are very expensive. Avoid including them in all of
CodeGen/ by moving the CodeGenPGO member behind a unqiue_ptr.

This reduces clang build time by 0.8%.

This is an expensive header, only include it where needed. Move some
functions out of line to achieve that.

This reduces time to build clang by ~0.5% in terms of instructions
retired.

I'm adding support for SPIR-V, so let's consolidate these checks.

---------

Signed-off-by: Sarnie, Nick <nick.sarnie@intel.com>

This pull request is the third part of an ongoing effort to extends PGO
instrumentation to GPU device code and depends on
https://github.com/llvm/llvm-project/pull/93365. This PR makes the
following changes:

- Allows PGO flags to be supplied to GPU targets
- Pulls version global from device
- Modifies `__llvm_write_custom_profile` and `lprofWriteDataImpl` to
allow the PGO version to be overridden

`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

Identified with misc-include-cleaner.

Don't call raw_string_ostream::flush(), which is essentially a no-op.
As specified in the docs, raw_string_ostream is always unbuffered