close nim-lang#15955; add a test case (nim-lang#20414)

tests/misc/m15955.nim

@@ -0,0 +1,4 @@
+proc add*(a, b: int): int {.cdecl, exportc.} =
+    a + b
+proc sub*(a, b: int): int {.cdecl, exportc.} =
+    a - b

tests/misc/m15955_main.nim

@@ -0,0 +1,11 @@
+import stdtest/specialpaths
+import std/os
+
+const buildLib = buildDir / "libD20220923T19380"
+
+{.passL: buildLib.}
+proc add*(a, b: int):int {.cdecl, importc.}
+proc sub*(a, b: int):int {.cdecl, importc.}
+
+echo add(10, 5)
+echo sub(10, 5)

tests/misc/t15955.nim

@@ -0,0 +1,22 @@
+discard """
+joinable: false
+"""
+
+import stdtest/specialpaths
+import std/[osproc, strformat, os]
+
+const
+  nim = getCurrentCompilerExe()
+  buildLib = buildDir / "libD20220923T19380"
+  currentDir = splitFile(currentSourcePath).dir
+  file = currentDir / "m15955.nim"
+  main = currentDir / "m15955_main.nim"
+
+
+proc runCmd(cmd: string) =
+  let (msg, code) = execCmdEx(cmd)
+  doAssert code == 0, msg
+
+
+runCmd fmt"{nim} c -o:{buildLib} --nomain --nimMainPrefix:libA -f --app:staticlib {file}"
+runCmd fmt"{nim} c -r {main}"