In C++20, the compiler will synthesize a version of the operator
with its arguments reversed to ease commutativity. This reversed
version is ambiguous with the hand-written operator when the
argument is const but `this` isn't.
Teach CachedDiagnosticsProcessor to replay diagnostics for all consumers
with a different path using a path prefix map. This allows diagnostics
to be replayed for the actual path on disk after the scanner
canonicalized the path for compilation.
Rename `-enable-cas` to `-compile-cache-job` to align with clang option
names and promote that to a new driver only flag.
Few other additions to driver flag for caching behaviors:
* `-compile-cache-remarks`: now cache hit/miss remarks are guarded behind
this flag
* `-compile-cache-skip`: skip replaying from the cache. Useful as a
debugging tool to do the compilation using CAS inputs even the output
is a hit from the cache.
When using a FileSpecificDiagConsumer, the source file that doesn't have
any diagnostics need to exist in the source manager for the consumer to
be successfully created.
Add a CachedDiagnosticsProcessor that is a DiagConsumer can capture all
the diagnostics during a compilation, serialized them into CAS with a
format that can be replayed without re-compiling.
