mingw: add the debug.issue1481 config setting to help debug further

In case that the previous commit does not quite fix things, let's add
some debug code that is guarded by the special-purpose `debug.issue1481`
config setting.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

compat/mingw.c

@@ -243,9 +243,15 @@ static enum hide_dotfiles_type hide_dotfiles = HIDE_DOTFILES_DOTGITONLY;
 static char *unset_environment_variables;
 int core_fscache;
 int core_long_paths;
+int debug_1481;
 
 int mingw_core_config(const char *var, const char *value, void *cb)
 {
+	if (!strcmp(var, "debug.issue1481")) {
+		debug_1481 = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "core.hidedotfiles")) {
 		if (value && !strcasecmp(value, "dotgitonly"))
 			hide_dotfiles = HIDE_DOTFILES_DOTGITONLY;
@@ -1752,15 +1758,18 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 	 */
 	if (!ret && restrict_handle_inheritance && stdhandles_count) {
 		DWORD err = GetLastError();
+		if (debug_1481) warning("error: %d", (int)err);
 		if (err == ERROR_NO_SYSTEM_RESOURCES ||
-		    err == ERROR_INVALID_HANDLE) {
+		    err == ERROR_INVALID_HANDLE || debug_1481) {
 			restrict_handle_inheritance = 0;
 			flags &= ~EXTENDED_STARTUPINFO_PRESENT;
 			ret = CreateProcessW(*wcmd ? wcmd : NULL, wargs, NULL,
 					     NULL, TRUE, flags, wenvblk,
 					     dir ? wdir : NULL,
 					     &si.StartupInfo, &pi);
+			if (debug_1481) warning("spawn2 %s, err: %d", ret ? "successful" : "failed", (int)GetLastError());
 		}
+		else error("spawn2 not even attempted");
 	}
 
 	if (!ret)