Fix link cxx object file error when building wamrc (#1794)

Author: wenyongh

wamr-compiler/CMakeLists.txt

@@ -109,7 +109,9 @@ if (CMAKE_SIZEOF_VOID_P EQUAL 8)
     if (NOT WAMR_BUILD_PLATFORM STREQUAL "windows")
       # Add -fPIC flag if build as 64-bit
       set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fPIC")
+      set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fPIC")
       set (CMAKE_SHARED_LIBRARY_LINK_C_FLAGS "${CMAKE_SHARED_LIBRARY_LINK_C_FLAGS} -fPIC")
+      set (CMAKE_SHARED_LIBRARY_LINK_CXX_FLAGS "${CMAKE_SHARED_LIBRARY_LINK_CXX_FLAGS} -fPIC")
     endif ()
   else ()
     add_definitions (-m32)