Everywhere there's a `SWIFT_MODULE_DEPENDS_LINUX Glibc`, there should be
a corresponding `SWIFT_MODULE_DEPENDS_LINUX_STATIC Musl`.
This usually won't bite us, depending on build order and parallelism, but
I hit one of these yesterday so went looking to see if there were any
others.
rdar://136208589
Friend PR: apple/swift-experimental-string-processing#282.
Also remove the `-enable-experimental-pairwise-build-block` flag when building regex modules as the feature is already on by default.
As the _MatchingEngine module no longer contains the matching engine, this patch renames this module to describe its role more accurately. Because this module primarily contains the AST and the regex parsing logic, I propose we rename it to "_RegexParser".
Also renames the ExperimentalRegex module in SwiftCompilerSources to _RegexParser for consistency. This would prevent errors if sources in _RegexParser used qualified lookup with the module name.
