workaround for openbsd to unblock ctffi testing

tests/trunner.nim

@@ -6,7 +6,7 @@ discard """
 ## tests that don't quite fit the mold and are easier to handle via `execCmdEx`
 ## A few others could be added to here to simplify code.
 
-import std/[strformat,os,osproc,strutils]
+import std/[strformat,os,osproc]
 
 const nim = getCurrentCompilerExe()
 
@@ -25,22 +25,36 @@ proc runCmd(file, options = ""): auto =
 
 when defined(nimHasLibFFIEnabled):
   block: # mevalffi
-    let (output, exitCode) = runCmd("vm/mevalffi.nim", "--experimental:compiletimeFFI")
-    let expected = """
+    when defined(openbsd):
+      #[
+      openbsd defines `#define stderr (&__sF[2])` which makes it cumbersome
+      for dlopen'ing inside `importcSymbol`. Instead of adding special rules
+      inside `importcSymbol` to handle this, we disable just the part that's
+      not working and will provide a more general, clean fix in future PR.
+      ]#
+      var opt = "-d:nimEvalffiStderrWorkaround"
+      let prefix = ""
+    else:
+      var opt = ""
+      let prefix = """
 hello world stderr
 hi stderr
-foo
+"""
+    let (output, exitCode) = runCmd("vm/mevalffi.nim", fmt"{opt} --experimental:compiletimeFFI")
+    let expected = fmt"""
+{prefix}foo
 foo:100
 foo:101
 foo:102:103
 foo:102:103:104
 foo:0.03:asdf:103:105
-ret={s1:foobar s2:foobar age:25 pi:3.14}
+ret=[s1:foobar s2:foobar age:25 pi:3.14]
 """
     doAssert output == expected, output
     doAssert exitCode == 0
 
 else: # don't run twice the same test
+  import std/[strutils]
   template check(msg) = doAssert msg in output, output
 
   block: # mstatic_assert

tests/vm/mevalffi.nim

@@ -42,7 +42,7 @@ proc fun() =
     let num = c_snprintf(buffer2, n, "s1:%s s2:%s age:%d pi:%g", s, s, age, 3.14)
     let numExp = 34 
     doAssert num == numExp
-    c_printf("ret={%s}\n", buffer2)
+    c_printf("ret=[%s]\n", buffer2)
     c_free(buffer2)
 
   block: # c_printf bug
@@ -61,10 +61,11 @@ static:
   fun()
 fun()
 
-import system/ansi_c
-block:
-  proc fun2()=
-    c_fprintf(cstderr, "hello world stderr\n")
-    write(stderr, "hi stderr\n")
-  static: fun2()
-  fun2()
+when not defined nimEvalffiStderrWorkaround:
+  import system/ansi_c
+  block:
+    proc fun2()=
+      c_fprintf(cstderr, "hello world stderr\n")
+      write(stderr, "hi stderr\n")
+    static: fun2()
+    fun2()