mingw: remove no-asynchronous-unwind-tables (#9963)

Summary:
This default is generally incompatible with other parts of mingw, and
can be applied by outside users as-needed.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9963

Reviewed By: akankshamahajan15

Differential Revision: D36302813

Pulled By: ajkr

fbshipit-source-id: 9456b41a96bde302bacbc39e092ccecfcb42f34f

CMakeLists.txt

@@ -194,7 +194,7 @@ else()
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wstrict-prototypes")
   endif()
   if(MINGW)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-format -fno-asynchronous-unwind-tables")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-format")
     add_definitions(-D_POSIX_C_SOURCE=1)
   endif()
   if(NOT CMAKE_BUILD_TYPE STREQUAL "Debug")