Fixed MinGW 7.3.0 shared library compile and link issues

added definition WIN32_WINNT=0x600
added missing libraries wsock32 ws2_32 crypt32

templates/CMakeLists.txt.template

@@ -266,6 +266,9 @@
     # TODO(jtattermusch): needed to build boringssl with VS2017, revisit later
     set(_gRPC_C_CXX_FLAGS "<%text>${_gRPC_C_CXX_FLAGS}</%text> /wd4987 /wd4774 /wd4819 /wd4996 /wd4619")
   endif()
+  if (MINGW)
+    add_definitions(-D_WIN32_WINNT=0x600)
+  endif()
   set(CMAKE_C_FLAGS "<%text>${CMAKE_C_FLAGS} ${_gRPC_C_CXX_FLAGS}</%text>")
   set(CMAKE_CXX_FLAGS "<%text>${CMAKE_CXX_FLAGS} ${_gRPC_C_CXX_FLAGS}</%text>")
 
@@ -308,7 +311,7 @@
     set(_gRPC_ALLTARGETS_LIBRARIES <%text>${CMAKE_DL_LIBS}</%text> rt m pthread)
   endif()
 
-  if(WIN32 AND MSVC)
+  if(WIN32)
     set(_gRPC_BASELIB_LIBRARIES wsock32 ws2_32 crypt32)
   endif()