Remove -Werror= CFLAGS that do not have the desired effect.

Originally committed as revision 11811 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1785,8 +1785,6 @@ check_cflags -Wpointer-arith
 check_cflags -Wredundant-decls
 check_cflags -Wno-pointer-sign
 check_cflags -Wcast-qual
-check_cflags -Werror=declaration-after-statement
-check_cflags -Werror=pointer-arith
 enabled extra_warnings && check_cflags -Winline
 
 # add some linker flags