add -Wno-pointer-sign to CFLAGS

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@7713 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -1776,6 +1776,7 @@ check_cflags -Wno-switch
 check_cflags -Wdisabled-optimization
 check_cflags -Wpointer-arith
 check_cflags -Wredundant-decls
+check_cflags -Wno-pointer-sign
 enabled extrawarnings && check_cflags -Winline
 
 # add some linker flags