fixes #10273 execShellCmd now returns nonzero when child killed with signal + other fixes (#10274)

* s/exitStatus(...)/exitStatusLikeShell(...)/
* fix #10273 execShellCmd now returns nonzero when child exits with signal
* test case for #10249 and explanation for the bug
* fix test failure
* add tests/nim.cfg

lib/pure/os.nim

@@ -1287,6 +1287,17 @@ proc moveFile*(source, dest: string) {.rtl, extern: "nos$1",
         discard tryRemoveFile(dest)
         raise
 
+proc exitStatusLikeShell*(status: cint): cint =
+  ## converts exit code from `c_system` into a shell exit code
+  when defined(posix) and not weirdTarget:
+    if WIFSIGNALED(status):
+      # like the shell!
+      128 + WTERMSIG(status)
+    else:
+      WEXITSTATUS(status)
+  else:
+    status
+
 proc execShellCmd*(command: string): int {.rtl, extern: "nos$1",
   tags: [ExecIOEffect], noNimScript.} =
   ## Executes a `shell command`:idx:.
@@ -1295,14 +1306,8 @@ proc execShellCmd*(command: string): int {.rtl, extern: "nos$1",
   ## line arguments given to program. The proc returns the error code
   ## of the shell when it has finished. The proc does not return until
   ## the process has finished. To execute a program without having a
-  ## shell involved, use the `execProcess` proc of the `osproc`
-  ## module.
-  when defined(macosx):
-    result = c_system(command) shr 8
-  elif defined(posix):
-    result = WEXITSTATUS(c_system(command))
-  else:
-    result = c_system(command)
+  ## shell involved, use `osproc.execProcess`.
+  result = exitStatusLikeShell(c_system(command))
 
 # Templates for filtering directories and files
 when defined(windows) and not weirdTarget: