Meta: Enable RELR relocations

Also add a check to serenity.sh to ensure that the toolchain is new
enough for this feature to work.

Meta/serenity.sh

@@ -242,6 +242,21 @@ build_toolchain() {
 
 ensure_toolchain() {
     [ -d "$TOOLCHAIN_DIR" ] || build_toolchain
+
+    # FIXME: Remove this check when most people have already updated their toolchain
+    if [ "$TOOLCHAIN_TYPE" = "GNU" ]; then
+        local ld_version
+        ld_version="$("$TOOLCHAIN_DIR"/bin/"$TARGET"-pc-serenity-ld -v)"
+        local expected_version="GNU ld (GNU Binutils) 2.38"
+        if [ "$ld_version" != "$expected_version" ]; then
+            echo "Your toolchain has an old version of binutils installed."
+            echo "    installed version: \"$ld_version\""
+            echo "    expected version:  \"$expected_version\""
+            echo "Please run $ARG0 rebuild-toolchain $TARGET to update it."
+            exit 1
+        fi
+    fi
+
 }
 
 delete_toolchain() {