`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

Part of #97952

This packs;
* `BitmapBytes`
* `BitmapMap`
* `CondIDMap`

into `MCDC::State`.

Part 3 of 3. This includes the MC/DC clang front-end components.

Differential Revision: https://reviews.llvm.org/D138849

This removes some uses of the deprecated `FileEntry::getName()`.

D83592 added comments to be part of skipped regions, and as part of that, it
also shrinks a skipped range if it spans a line that contains a non-comment
token. This is done by `adjustSkippedRange`.

The `adjustSkippedRange` currently runs on skipped regions that are not
comments, causing a 5min regression while building a big C++ files without any
comments.

Fix the compile time introduced in D83592 by tagging SkippedRange with kind
information and use that to decide what needs additional processing.

Differential Revision: https://reviews.llvm.org/D127338

These flags affect coverage mapping (-fcoverage-mapping), not
-fprofile-[instr-]generate so it makes more sense to use the
-fcoverage-* prefix.

Differential Revision: https://reviews.llvm.org/D97434

We currently always store absolute filenames in coverage mapping.  This
is problematic for several reasons. It poses a problem for distributed
compilation as source location might vary across machines.  We are also
duplicating the path prefix potentially wasting space.

This change modifies how we store filenames in coverage mapping. Rather
than absolute paths, it stores the compilation directory and file paths
as given to the compiler, either relative or absolute. Later when
reading the coverage mapping information, we recombine relative paths
with the working directory. This approach is similar to handling
ofDW_AT_comp_dir in DWARF.

Finally, we also provide a new option, -fprofile-compilation-dir akin
to -fdebug-compilation-dir which can be used to manually override the
compilation directory which is useful in distributed compilation cases.

Differential Revision: https://reviews.llvm.org/D95753

This reverts commit 97ec8fa5bb07e3f5bf25ddcb216b545cd3d03b65 since
the test is failing on some bots.