fixes #10943 (#10947)

compiler/cgen.nim

@@ -1619,7 +1619,10 @@ proc genModule(m: BModule, cfile: Cfile): Rope =
   add(result, m.s[cfsHeaders])
   add(result, genSectionEnd(cfsHeaders, m.config))
   add(result, genSectionStart(cfsFrameDefines, m.config))
-  add(result, m.s[cfsFrameDefines])
+  if m.s[cfsFrameDefines].len > 0:
+    add(result, m.s[cfsFrameDefines])
+  else:
+    add(result, "#define nimfr_(x, y)\n#define nimln_(x, y)\n")
   add(result, genSectionEnd(cfsFrameDefines, m.config))
 
   for i in countup(cfsForwardTypes, cfsProcs):

tests/constr/a_module.nim

@@ -0,0 +1,6 @@
+# a.nim
+{.push stackTrace: off.}
+proc foo*(): int =
+  var a {.global.} = 0
+  result = a
+{.pop.}

tests/constr/tglobal.nim

@@ -0,0 +1,7 @@
+discard """
+output: "0"
+"""
+
+# b.nim
+import a_module
+echo foo()