Add -Wno-void-pointer-to-enum-cast (we use this hack in tests)

Refs: https://reviews.llvm.org/D75758

CMakeLists.txt

@@ -295,6 +295,9 @@ if (${GNUC})
          -Wlogical-op
 
          -Wwrite-strings
+
+         # we use this hack in tests
+         -Wno-void-pointer-to-enum-cast
     )
 
     if (${CLANG})

configure.ac

@@ -772,6 +772,7 @@ if test x$enable_gcc_warnings != xno && test "$GCC" = "yes"; then
 
   dnl Disable warnings for unused paramaters
   AX_CHECK_COMPILE_FLAG([-Wno-unused-parameter], [CFLAGS="$CFLAGS -Wno-unused-parameter"],[],[-Werror])
+  AX_CHECK_COMPILE_FLAG([-Wno-void-pointer-to-enum-cast], [CFLAGS="$CFLAGS -Wno-void-pointer-to-enum-cast"],[],[-Werror])
 
   AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [
   #if !defined(__clang__)