avoid the annoying xpdf warning about string literal conversion to error()

Clang quotes it in the warning message, and tinderbox log parser highlights
every single of the warnings because of the 'error'.

Change-Id: I6a2addc6817d05d18dcc1985ecaca0b110045ecf

xpdf/makefile.mk

@@ -48,7 +48,7 @@ dummy:
 
 TARFILE_NAME=xpdf-3.02
 TARFILE_MD5=599dc4cc65a07ee868cf92a667a913d2
-PATCH_FILES=$(TARFILE_NAME).patch xpdf-3.02-ooopwd.patch xpdf-3.02-gfxColorMaxComps.patch
+PATCH_FILES=$(TARFILE_NAME).patch xpdf-3.02-ooopwd.patch xpdf-3.02-gfxColorMaxComps.patch xpdf-no-writable-literals.patch
 
 CONFIGURE_DIR=
 BUILD_DIR=$(CONFIGURE_DIR)

xpdf/xpdf-no-writable-literals.patch

+--- misc/xpdf-3.02/xpdf/Error.h.sav	2007-02-27 23:05:52.000000000 +0100
++++ misc/build/xpdf-3.02/xpdf/Error.h	2012-10-09 23:24:12.002455791 +0200
+@@ -18,6 +18,6 @@
+ #include <stdio.h>
+ #include "config.h"
+ 
+-extern void CDECL error(int pos, char *msg, ...);
++extern void CDECL error(int pos, const char *msg, ...);
+ 
+ #endif
+--- misc/build/xpdf-3.02/xpdf/Error.cc.sav	2007-02-27 23:05:52.000000000 +0100
++++ misc/build/xpdf-3.02/xpdf/Error.cc	2012-10-09 23:24:27.813569809 +0200
+@@ -18,7 +18,7 @@
+ #include "GlobalParams.h"
+ #include "Error.h"
+ 
+-void CDECL error(int pos, char *msg, ...) {
++void CDECL error(int pos, const char *msg, ...) {
+   va_list args;
+ 
+   // NB: this can be called before the globalParams object is created