The bare "PATTERN" argument by default does nothing, you need either
"EXCLUDE" or "FILES_MATCHING" to make it do something. This likely
wasn't previously a problem because clang is only installing headers,
but it should be fixed for robustness.
As a result of #33346 we are relying on the tool for the current target -- this will
work for the host architecture but will fail when crosscompiling.
Addresses rdar://66800239
Building of the diagnostic database to be done in three steps:
- Copy YAMLs from <source>/localization/diagnostics to <build>/share/swift/diagnostics
- Serialize English into <build>/share/swift/diagnostics
- Install everything (YAML and `.db`) from <build>/share/swift/diagnostics
to share/swift/diagnostics in toolchain