Remove special mingw handling, does not apply for msys2

CMakeLists.txt

@@ -209,7 +209,7 @@ else()
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -W -Wextra -Wall")
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wsign-compare -Wshadow -Wno-unused-parameter -Wno-unused-variable -Woverloaded-virtual -Wnon-virtual-dtor -Wno-missing-field-initializers -Wno-strict-aliasing")
   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")
@@ -869,12 +869,12 @@ if(WIN32)
     port/win/env_default.cc
     port/win/port_win.cc
     port/win/win_logger.cc)
-  if(NOT MINGW)
+#  if(NOT MINGW)
     # Mingw only supports std::thread when using
     # posix threads.
     list(APPEND SOURCES
       port/win/win_thread.cc)
-  endif()
+#  endif()
 if(WITH_XPRESS)
   list(APPEND SOURCES
     port/win/xpress_win.cc)