Enable the -Wshadow warning flag on C++ files

Bug: aomedia:3450
Fixed: aomedia:3450
Change-Id: I995142074ab6a53a5c6f1e052524a50cf3696f0a
diff --git a/build/cmake/aom_configure.cmake b/build/cmake/aom_configure.cmake
index ad33f9a..aaef2c3 100644
--- a/build/cmake/aom_configure.cmake
+++ b/build/cmake/aom_configure.cmake
@@ -344,6 +344,7 @@
   add_c_flag_if_supported("-Wimplicit-function-declaration")
   add_compiler_flag_if_supported("-Wlogical-op")
   add_compiler_flag_if_supported("-Wpointer-arith")
+  add_compiler_flag_if_supported("-Wshadow")
   add_compiler_flag_if_supported("-Wshorten-64-to-32")
   add_compiler_flag_if_supported("-Wsign-compare")
   add_compiler_flag_if_supported("-Wstring-conversion")
@@ -375,9 +376,6 @@
     add_compiler_flag_if_supported("-Wno-disabled-optimization")
   endif()
 
-  # Add -Wshadow only for C files to avoid massive gtest warning spam.
-  add_c_flag_if_supported("-Wshadow")
-
   # Add -Wundef only for C files to avoid massive gtest warning spam.
   add_c_flag_if_supported("-Wundef")