[Intel-gfx] build error with GCC5.1.1

[chunshan.zhu]

gcc5.1.1 generates an error at build time.

sna_accel.c: In function 'sna_poly_zero_line_blt':
sna_accel.c:9207:10: warning: variable 'intersects' set but not used 
[-Wunused-but-set-variable]
       bool intersects;
           ^
sna_accel.c:9107:6: warning: variable 'degenerate' set but not used 
[-Wunused-but-set-variable]
   bool degenerate = true;
       ^
   CC       sna_cpu.lo
In file included from /usr/include/string.h:635:0,
                  from /usr/include/xorg/os.h:53,
                  from /usr/include/xorg/misc.h:115,
                  from /usr/include/xorg/xf86str.h:37,
                  from sna.h:43,
                  from blt.c:32:
blt.c: In function 'memcpy_from_tiled_x__swizzle_9_10_11':
/usr/include/bits/string3.h:50:42: error: inlining failed in call to 
always_inline 'memcpy': optimization level attribute mismatch
  __NTH (memcpy (void *__restrict __dest, const void *__restrict __src,
                                           ^
blt.c:474:1314: error: called from here
In file included from /usr/include/string.h:635:0,
                  from /usr/include/xorg/os.h:53,
                  from /usr/include/xorg/misc.h:115,
                  from /usr/include/xorg/xf86str.h:37,
                  from sna.h:43,
                  from blt.c:32:
/usr/include/bits/string3.h:50:42: error: inlining failed in call to 
always_inline 'memcpy': optimization level attribute mismatch
  __NTH (memcpy (void *__restrict __dest, const void *__restrict __src,
                                           ^
blt.c:474:1605: error: called from here
In file included from /usr/include/string.h:635:0,
                  from /usr/include/xorg/os.h:53,
                  from /usr/include/xorg/misc.h:115,
                  from /usr/include/xorg/xf86str.h:37,
                  from sna.h:43,
                  from blt.c:32:
/usr/include/bits/string3.h:50:42: error: inlining failed in call to 
always_inline 'memcpy': optimization level attribute mismatch
  __NTH (memcpy (void *__restrict __dest, const void *__restrict __src,
                                           ^
blt.c:474:1865: error: called from here
Makefile:650: recipe for target 'blt.lo' failed