After adopting the stable/20221013 clang branch, ClangImporter started seeing out-of-date identifiers in macros where it previously never had. Force these identifiers to update themselves before we read the macro definition out of them.
Fixes rdar://104456939.
While most -Xcc options turn into options that affect the Clang module
cache hash, some, like search paths, do not, and that can have a
drastic effect on PCH contents. When combined with places where Xcode
will modify invocations to add extra -Xcc options (see
rdar://problem/23297285), this can lead to crashes where the
modified-invocation PCH is used to compile source files in incremental
mode, and then the original, non-precompiled bridging header is used
for module merging. Let's just be conservative and include -Xcc
options in the Swift-side PCH uniqueness hash.
rdar://problem/33837253
For the multiple-files mode -emit-pch is still invoked in separate frontend invocation but with using a persistent PCH.
Subsequent frontend invocations use the persistent PCH but they don't need to validate it.
For all-files mode (e.g. WMO) the frontend invocation uses a persistent PCH that it also validates.
