patch 8.0.0409: set_progpath is defined but not always used

Problem:    set_progpath is defined but not always used
Solution:   Adjust #ifdef.
diff --git a/src/main.c b/src/main.c
index 1da2b84..2575e82 100644
--- a/src/main.c
+++ b/src/main.c
@@ -3528,7 +3528,7 @@
 
 #endif
 
-#ifndef NO_VIM_MAIN
+#if !defined(NO_VIM_MAIN) && defined(FEAT_EVAL)
     static void
 set_progpath(char_u *argv0)
 {