fix #19680; check if stderr is static (#19709)

(cherry picked from commit 26bcf18)

Author: ringabout

compiler/vmgen.nim

@@ -1497,7 +1497,7 @@ proc checkCanEval(c: PCtx; n: PNode) =
   # proc foo() = var x ...
   let s = n.sym
   if {sfCompileTime, sfGlobal} <= s.flags: return
-  if s.importcCondVar: return
+  if compiletimeFFI in c.config.features and s.importcCondVar: return
   if s.kind in {skVar, skTemp, skLet, skParam, skResult} and
       not s.isOwnedBy(c.prc.sym) and s.owner != c.module and c.mode != emRepl:
     # little hack ahead for bug #12612: assume gensym'ed variables

tests/misc/tvarious1.nim

@@ -46,3 +46,13 @@ echo value
 var ys = @[4.1, 5.6, 7.2, 1.7, 9.3, 4.4, 3.2]
 #var x = int(ys.high / 2) #echo ys[x] # Works
 echo ys[int(ys.high / 2)] # Doesn't work
+
+
+# bug #19680
+var here = ""
+when stderr is static:
+  doAssert false
+else:
+  here = "works"
+
+doAssert here == "works"