CMake: Disable async unwind tables on mingw+preserve_all

From the comment
[here](https://github.com/FEX-Emu/FEX/pull/6094#issuecomment-6626133724)
apparently there is a bug where async unwind tables and preserve_all
conflicts under mingw. So...just disable it. Easy.

CMakeLists.txt

@@ -261,6 +261,10 @@ if (HAS_CLANG_PRESERVE_ALL)
     set(HAS_CLANG_PRESERVE_ALL FALSE)
   else()
     message(STATUS "Has clang::preserve_all")
+    if (MINGW)
+      message(STATUS "Disabling asynchronous-unwind-tables due to bug with preserve_all and mingw")
+      add_compile_options(-fno-asynchronous-unwind-tables)
+    endif()
   endif()
 endif()