Fix Werror handling in build script (#7562)

# About the pull request

This PR partially ports
tgstation/tgstation#83015 fixing warnings not
getting treated as errors due to a regex error. We want Werror to catch
common things like unused variables in CI testing.

Removes an unused squad var causing warnings.

# Explain why it's good for the game

More robust code

# Testing Photographs and Procedure
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functioning successfully, ideally including edge cases. -->

<!-- !! If you are modifying sprites, you **must** include one or more
in-game screenshots or videos of the new sprites. !! -->


https://github.com/cmss13-devs/cmss13/actions/runs/11770975974/job/32784168250?pr=7562

# Changelog
No player facing changes.

code/datums/factions/upp.dm

@@ -5,7 +5,6 @@
 /datum/faction/upp/modify_hud_holder(image/holder, mob/living/carbon/human/H)
 	var/hud_icon_state
 	var/obj/item/card/id/ID = H.get_idcard()
-	var/datum/squad/squad = H.assigned_squad
 	var/_role
 	if(H.mind)
 		_role = H.job

tools/build/lib/byond.js

@@ -174,14 +174,18 @@ export const DreamMaker = async (dmeFile, options = {}) => {
   testOutputFile(`${dmeBaseName}.rsc`);
   const runWithWarningChecks = async (dmPath, args) => {
     const execReturn = await Juke.exec(dmPath, args);
-    const ignoredWarningCodes = options.ignoreWarningCodes ?? [];
-    const reg =
-      ignoredWarningCodes.length > 0
-        ? new RegExp(`\d+:warning: (?!(${ignoredWarningCodes.join("|")}))`)
-        : /\d+:warning: /;
-    if (options.warningsAsErrors && execReturn.combined.match(reg)) {
-      Juke.logger.error(`Compile warnings treated as errors`);
-      throw new Juke.ExitCode(2);
+    if(options.warningsAsErrors){
+      const ignoredWarningCodes = options.ignoreWarningCodes ?? [];
+      if(ignoredWarningCodes.length > 0 ){
+        Juke.logger.info('Ignored warning codes:', ignoredWarningCodes.join(', '));
+      }
+      const base_regex = '\\d+:warning( \\([a-z_]*\\))?:'
+      const with_ignores = `\\d+:warning( \\([a-z_]*\\))?:(?!(${ignoredWarningCodes.map(x => `.*${x}.*$`).join('|')}))`
+      const reg = ignoredWarningCodes.length > 0 ? new RegExp(with_ignores, "m") : new RegExp(base_regex,"m")
+      if (options.warningsAsErrors && execReturn.combined.match(reg)) {
+        Juke.logger.error(`Compile warnings treated as errors`);
+        throw new Juke.ExitCode(2);
+      }
     }
     return execReturn;
   };