[clang] [Clang][Cygwin] attempt to fix building shared libclang. (PR #138351)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

Offhand, I don't quite know here. Which configurations is this about? For mingw, the only cases I'm familiar with is building with `LLVM_LINK_LLVM_DYLIB=ON`, which iirc implicitly enables a corresponding one for Clang too. Not sure which of the local variables here that maps to without trying and tracing it.

Building that kind of dylib used to work with GCC, but these days it probably hits the limit on the number of exported symbols (initially in libLLVM-*.dll), unless you reduce the number of enabled targets a lot.

https://github.com/llvm/llvm-project/pull/138351