VM FFI: write(stderr, msg) and fprintf(cstderr, msg) now work at CT (#13083)

tests/vm/tevalffi.nim

@@ -8,6 +8,8 @@ foo:102:103
 foo:102:103:104
 foo:0.03:asdf:103:105
 ret={s1:foobar s2:foobar age:25 pi:3.14}
+hello world stderr
+hi stderr
 '''
   output: '''
 foo
@@ -17,6 +19,8 @@ foo:102:103
 foo:102:103:104
 foo:0.03:asdf:103:105
 ret={s1:foobar s2:foobar age:25 pi:3.14}
+hello world stderr
+hi stderr
 '''
   disabled: "true"
 """
@@ -76,6 +80,15 @@ proc fun() =
     if false:
       c_printf("foo2:a=%d\n", a2)
 
+
 static:
   fun()
 fun()
+
+when true:
+  import system/ansi_c
+  proc fun2()=
+    c_fprintf(cstderr, "hello world stderr\n")
+    write(stderr, "hi stderr\n")
+  static: fun2()
+  fun2()