cc-wrapper: warn about cross-compile only with non-default (#379593)

pkgs/build-support/cc-wrapper/add-clang-cc-cflags-before.sh

@@ -1,15 +1,35 @@
 needsTarget=true
+targetValue=""
+
+declare -i n=0
+nParams=${#params[@]}
+while (("$n" < "$nParams")); do
+    p=${params[n]}
+    v=${params[n + 1]:-} # handle `p` being last one
+    n+=1
 
-for p in "${params[@]}"; do
     case "$p" in
-    -target | --target=*)
+    -target)
+        if [ -z "$v" ]; then
+            echo "Error: -target requires an argument" >&2
+            exit 1
+        fi
         needsTarget=false
-
-        echo "Warning: supplying the --target argument to a nix-wrapped compiler may not work correctly - cc-wrapper is currently not designed with multi-target compilers in mind. You may want to use an un-wrapped compiler instead." >&2
+        targetValue=$v
+        # skip parsing the value of -target
+        n+=1
+        ;;
+    --target=*)
+        needsTarget=false
+        targetValue="${p#*=}"
         ;;
     esac
 done
 
+if ! $needsTarget && [[ "$targetValue" != "@defaultTarget@" ]]; then
+    echo "Warning: supplying the --target $targetValue != @defaultTarget@ argument to a nix-wrapped compiler may not work correctly - cc-wrapper is currently not designed with multi-target compilers in mind. You may want to use an un-wrapped compiler instead." >&2
+fi
+
 if $needsTarget && [[ $0 != *cpp ]]; then
     extraBefore+=(-target @defaultTarget@ @machineFlags@)
 fi