CI: Don't fail check-symbols if symbol is defiend somewhere else

Author: https://github.com/itamar8910
Commit: https://github.com/SerenityOS/serenity/commit/4cb38f6dd8c
Pull-request: https://github.com/SerenityOS/serenity/pull/5808
Issue: https://github.com/SerenityOS/serenity/issues/5758

Meta/check-symbols.sh

@@ -11,8 +11,12 @@ cd "$script_path/.." || exit 1
 FORBIDDEN_SYMBOLS="__cxa_guard_acquire __cxa_guard_release"
 LIBC_PATH="Build/Userland/Libraries/LibC/libc.a"
 for forbidden_symbol in $FORBIDDEN_SYMBOLS; do
-    # check if symbol is undefined
-    if nm $LIBC_PATH | grep "U $forbidden_symbol" ; then
+    # check if there's an undefined reference to the symbol & it is not defined anywhere else in the library
+    nm $LIBC_PATH | grep "U $forbidden_symbol"
+    APPEARS_AS_UNDEFINED=$?
+    nm $LIBC_PATH | grep "T $forbidden_symbol"
+    APPEARS_AS_DEFINED=$?
+    if [ $APPEARS_AS_UNDEFINED -eq 0 ] && [ ! $APPEARS_AS_DEFINED -eq 0 ]; then
         echo "Forbidden undefined symbol in LibC: $forbidden_symbol"
         echo "See comment in Meta/check-symbols.sh for more info"
         exit 1