Don't force libc++ with clang (#1984)

Clang works with libstdc++.

src/CMakeData-gtk.cmake

@@ -8,10 +8,6 @@ add_library("GtkModule"
             "arch/LoadingWindow/LoadingWindow_GtkModule.h")
 
 sm_add_compile_flag("GtkModule" "-std=${SM_CPP_STANDARD}")
-if(CMAKE_CXX_COMPILER MATCHES "clang")
-  sm_add_compile_flag("GtkModule" "-stdlib=libc++")
-  set_target_properties("GtkModule" PROPERTIES LINK_FLAGS "-stdlib=libc++")
-endif()
 
 # It is normally not appropriate to set the prefix to the empty string. This is
 # to maintain compatibility with the current source. At some point, it may be

src/CMakeLists.txt

@@ -390,12 +390,6 @@ else() # Linux
   endif()
 
   sm_add_compile_flag("${SM_EXE_NAME}" "-std=${SM_CPP_STANDARD}")
-  if(CMAKE_CXX_COMPILER MATCHES "clang")
-    sm_add_compile_flag("${SM_EXE_NAME}" "-stdlib=libc++")
-    set_target_properties("${SM_EXE_NAME}"
-                          PROPERTIES LINK_FLAGS "-stdlib=libc++")
-    sm_add_compile_flag("jsoncpp" "-stdlib=libc++")
-  endif()
 endif()
 
 set_property(TARGET "${SM_EXE_NAME}" PROPERTY FOLDER "Internal Libraries")