methods of disabling glyphid cache prefill

Two methods are now provided for slow ports/platforms that
need to do this for performance reasons.

Hopefully, this will avoid proliferation of more platform-specific
conditional code within initoptions_init().

Method (1): #define DISABLE_GLYPHID_CACHE_PREFILL in platform/OS's
            include/*conf.h.

or

Method (2): set gd.disable_glyphid_cache_prefill = TRUE in startup code
            after decl_global_init(), and prior to initoptions_init().
	    It has to be done after decl_global_init() because
	    decl_global_init() sets the value to its initialization
	    default.

include/decl.h

@@ -344,6 +344,7 @@ struct instance_globals_d {
     /* new */
     boolean deferred_showpaths;
     char *deferred_showpaths_dir;
+    boolean disable_glyphid_cache_prefill;
 
     boolean havestate;
 };

src/decl.c

@@ -313,6 +313,7 @@ static const struct instance_globals_d g_init_d = {
     FALSE, /* decor_levitate_override */
     FALSE, /* deferred_showpaths */
     NULL,  /* deferred_showpaths_dir  */
+    FALSE, /* disable_glyphid_cache_prefill */
     TRUE, /* havestate*/
 };
 
@@ -1184,6 +1185,9 @@ decl_globals_init(void)
 
     gu.urole = urole_init_data;
     gu.urace = urace_init_data;
+#ifdef DISABLE_GLYPHID_CACHE_PREFILL
+    gd.disable_glyphid_cache_prefill = TRUE;
+#endif
 }
 
 /* fields in 'hands_obj' don't matter, just its distinct address */

src/options.c

@@ -7151,8 +7151,9 @@ initoptions_init(void)
             gc.cmdline_windowsys = NULL;
     }
 
-    /* make any symbol parsing quicker */
-    if (!glyphid_cache_status())
+    /* make any symbol parsing quicker, but only if
+     * gd.disable_glyphid_cache_prefill is not set to TRUE */
+    if (!glyphid_cache_status() && !gd.disable_glyphid_cache_prefill)
         fill_glyphid_cache();
 
     /* set up the command parsing */