[Clang][Cygwin] Disable shared libs on Cygwin by default (#138119)
This change follows MinGW decisions, otherwise build with GCC fail with:
```
FAILED: bin/msys-clang-cpp-21.0git.dll lib/libclang-cpp.dll.a
...
/usr/lib/gcc/x86_64-pc-msys/13.3.0/../../../../x86_64-pc-msys/bin/ld: error: export ordinal too large: 92250
```
Co-authored-by: jeremyd2019 <github@jdrake.com>