This patch avoids the two gcc warnings
		../../libXft-2.1.13/src/xftglyphs.c:174: warning: implicit declaration of function `FT_GlyphSlot_Embolden'
		../../libXft-2.1.13/src/xftglyphs.c:174: warning: nested extern declaration of `FT_GlyphSlot_Embolden'

	However, quoting from ftsynth.h (freetype2-2.3.7)
	        WARNING, THIS IS ALPHA CODE, THIS API
	    IS DUE TO CHANGE UNTIL STRICTLY NOTIFIED BY THE
	            FREETYPE DEVELOPMENT TEAM
	and just before the declaration of FT_GlyphSlot_Embolden
	  /* Do not use this function directly!  Copy the code to */
	  /* your application and modify it to suit your need.    */

	Conclusion: Shouldn't one just do that (i.e., copy the code)?

diff -ur libXft-2.1.13.orig/src/xftglyphs.c libXft-2.1.13/src/xftglyphs.c
--- libXft-2.1.13.orig/src/xftglyphs.c	2008-05-12 23:31:03.000000000 +0200
+++ libXft-2.1.13/src/xftglyphs.c	2008-10-07 13:04:57.000000000 +0200
@@ -22,6 +22,9 @@
 
 #include "xftint.h"
 #include <freetype/ftoutln.h>
+#if HAVE_FT_GLYPHSLOT_EMBOLDEN
+#include <freetype/ftsynth.h>
+#endif
 
 static const int    filters[3][3] = {
     /* red */