throw an error is PREFIX isnt defined on X11 systems. defaults to /usr/local

intern/ghost/SConscript

@@ -21,6 +21,8 @@ if window_system in ('linux2', 'openbsd3', 'sunos5', 'freebsd7', 'freebsd8', 'fr
             sources.remove('intern' + os.sep + f + 'Carbon.cpp')
         except ValueError:
             pass
+    defs += ['PREFIX=\\"/usr/local/\\"']
+
 elif window_system in ('win32-vc', 'win32-mingw', 'cygwin', 'linuxcross', 'win64-vc'):
     for f in pf:
         try:

intern/ghost/intern/GHOST_SystemX11.cpp

@@ -68,7 +68,7 @@
 #include <cstdlib> // for exit
 
 #ifndef PREFIX
-#  define PREFIX "/usr/local"
+#error "PREFIX not defined"
 #endif
 
 typedef struct NDOFPlatformInfo {