patch 9.1.0345: Problem: gvimrc not sourced from XDG_CONFIG_HOME

Problem:  gvimrc not sourced from XDG_CONFIG_HOME (after v9.1.0327)
Solution: Also try to source from ~/.config/vim/gvimrc and
          $XDG_CONFIG_HOME/vim/gvimrc (Maxim Kim)

fixes: #14567
closes: #14568

Signed-off-by: Maxim Kim <habamax@haba-debian.habamax>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/os_unix.h b/src/os_unix.h
index 67dad2e..6efd8ce 100644
--- a/src/os_unix.h
+++ b/src/os_unix.h
@@ -279,6 +279,12 @@
 # ifndef USR_GVIMRC_FILE3
 #  define USR_GVIMRC_FILE3  "sys$login:_gvimrc"
 # endif
+#else
+# ifndef USR_GVIMRC_FILE3
+#  define USR_GVIMRC_FILE3 (mch_getenv("XDG_CONFIG_HOME") \
+	? "$XDG_CONFIG_HOME/vim/gvimrc" \
+	: "~/.config/vim/gvimrc")
+# endif
 #endif
 
 #ifndef VIM_DEFAULTS_FILE