cmake: don't check c++ compiler flags for asan when CXX is not enabled

Backport of fd2b9c060291af8ba3388f18b3b0000e81e41643 to SDL2

CMakeLists.txt

@@ -3210,9 +3210,11 @@ macro(check_add_debug_flag FLAG SUFFIX)
         set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} ${FLAG}")
     endif()
 
-    check_cxx_compiler_flag(${FLAG} HAS_CXX_${SUFFIX})
-    if (HAS_CXX_${SUFFIX})
-        set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} ${FLAG}")
+    if(CMAKE_CXX_COMPILER)
+      check_cxx_compiler_flag(${FLAG} HAS_CXX_${SUFFIX})
+      if (HAS_CXX_${SUFFIX})
+          set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} ${FLAG}")
+      endif()
     endif()
 endmacro()
 
@@ -3231,18 +3233,20 @@ macro(asan_check_add_debug_flag2 ASAN_FLAG)
 
     set (STORED_REQLIBS ${CMAKE_REQUIRED_LIBRARIES})
     set (CMAKE_REQUIRED_LIBRARIES "${FLAG};asan")
-    check_c_compiler_flag (${FLAG} HAS_C_FLAG_${ASAN_FLAG})
-    check_cxx_compiler_flag (${FLAG} HAS_CXX_FLAG_${ASAN_FLAG})
-    set (CMAKE_REQUIRED_LIBRARIES ${STORED_REQLIBS})
 
+    check_c_compiler_flag (${FLAG} HAS_C_FLAG_${ASAN_FLAG})
     if (HAS_C_FLAG_${ASAN_FLAG})
         set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} ${FLAG}")
     endif()
 
-    if (HAS_CXX_${ASAN_FLAG})
-        set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} ${FLAG}")
+    if(CMAKE_CXX_COMPILER)
+      check_cxx_compiler_flag (${FLAG} HAS_CXX_FLAG_${ASAN_FLAG})
+      if (HAS_CXX_${ASAN_FLAG})
+          set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} ${FLAG}")
+      endif()
     endif()
 
+    set (CMAKE_REQUIRED_LIBRARIES ${STORED_REQLIBS})
     if(HAS_C_${ASAN_FLAG} OR HAS_CXX_${ASAN_FLAG})
       set(HAVE_ASAN ON)
     endif()