[clang] [Clang][Cygwin] Disable shared libs on Cygwin by default (PR #138119)

[via cfe-commits]

================
@@ -106,7 +106,8 @@ if (LLVM_EXPORTED_SYMBOL_FILE)
                      DEPENDS ${LIBCLANG_VERSION_SCRIPT_FILE})
 endif()
 
-if(LLVM_ENABLE_PIC OR (WIN32 AND NOT LIBCLANG_BUILD_STATIC))
+if((NOT (WIN32 OR CYGWIN) AND LLVM_ENABLE_PIC) OR
+  ((WIN32 OR CYGWIN) AND NOT LIBCLANG_BUILD_STATIC))
----------------
jeremyd2019 wrote:

as in,
```
if(LLVM_ENABLE_PIC OR ((WIN32 OR CYGWIN) AND NOT LIBCLANG_BUILD_STATIC))
```

https://github.com/llvm/llvm-project/pull/138119