fixes #21261; always checking nimTestErrorFlag in the main module (#21288)

* fixes #21261; always checking nimTestErrorFlag in the main module

* add a test

compiler/cgen.nim

@@ -1801,6 +1801,9 @@ proc genInitCode(m: BModule) =
 
     if optStackTrace in m.initProc.options and preventStackTrace notin m.flags:
       prc.add(deinitFrame(m.initProc))
+  elif sfMainModule in m.module.flags and m.config.exc == excGoto:
+    if getCompilerProc(m.g.graph, "nimTestErrorFlag") != nil:
+      m.appcg(prc, "\t#nimTestErrorFlag();$n", [])
 
   prc.addf("}$N", [])
 

tests/exception/m21261.nim

@@ -0,0 +1 @@
+raise (ref Exception)(msg: "something")

tests/exception/t21261.nim

@@ -0,0 +1,9 @@
+discard """
+  exitcode: 1
+  outputsub: '''
+m21261.nim(1)            m21261
+Error: unhandled exception: something [Exception]
+'''
+"""
+
+import m21261