MIPS: Fix GCC-4.6 'set but not used' warning in ieee754int.h

GCC-4.6 can find more unused code than previous versions could.

In the case of arch/mips/math-emu/ieee754int.h, the COMPXSP and
COMPXDP macros are used in several places, but a couple of them leave
xs unused.  The easiest thing to do is mark it as __maybe_unused to
quiet the warning.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2032/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/math-emu/ieee754int.h

@@ -70,7 +70,7 @@
 
 
 #define COMPXSP \
-  unsigned xm; int xe; int xs; int xc
+  unsigned xm; int xe; int xs __maybe_unused; int xc
 
 #define COMPYSP \
   unsigned ym; int ye; int ys; int yc
@@ -104,7 +104,7 @@
 
 
 #define COMPXDP \
-u64 xm; int xe; int xs; int xc
+u64 xm; int xe; int xs __maybe_unused; int xc
 
 #define COMPYDP \
 u64 ym; int ye; int ys; int yc