This is a follow-up after the change that enabled Cxx and CxxStdlib overlays on macCatalyst: https://github.com/swiftlang/swift/pull/74994.
The compiler relies on the presence of these shim libraries in the toolchain.
rdar://135275773
Mostly this just means adding `Musl` as a module dependency of various
things and making sure that we build things for `swift_static` even
if `SWIFT_BUILD_STATIC_STDLIB` isn't enabled.
There's also a slight difference in the declaration of `memcmp()`;
musl's declaration is more like the one we have on Darwin.
rdar://123508245
This moves `libcxxshim.modulemap`, `libcxxshim.h` and `libcxxstdlibshim.h` from `*.xctoolchain/usr/lib/swift/macosx/arm64e` to `*.xctoolchain/usr/lib/swift/macosx` to simplify distribution.
rdar://110788977
This fixes the `no such module 'CxxStdlibShim'` error when building CxxStdlib for armv7k.
For watchOS, armv7k is included in `${SWIFT_SDK_${sdk}_MODULE_ARCHITECTURES}` but not in `${SWIFT_SDK_${sdk}_ARCHITECTURES}`.
rdar://108206099
The modulemap and header files target was added to `ALL`, which works
when invoking the build thru the `build-script`, but make some test fail
when doing a manual configuration and later doing
`check-swift-validation` or similar, because the modulemap/header were
not copied into the build directory.
Follow a pattern similar to the one in GlibC (which this file seemed to
be prepared for, since the `libcxxshim_modulemap_target_list` variable
was already there), create a global target for all the modulemap/headers
of each SDK and add that global target as a dependency of sdk-overlay
(which is a dependency of check-swift-validation and others).
