Fix build under g++-4.9, SunOS 5.11 i386 i86pc Solaris

[Naios]

• thanks @VolodymyrLavrenchuk for pointing this out.

Fixes a build error on SunOS 5.11 caused through a duplicated variable name (probably in system headers).

[vitaut]

Merged, thanks.

For future reference, here's the error (copied from http://pastebin.com/JkxfgLZD):

/mnt/software/solaris/wow/TrinityCore_3_3_5a/build# make
In file included from /usr/include/sys/ucontext.h:36:0,
                 from /usr/include/sys/signal.h:245,
                 from /usr/include/sys/procset.h:42,
                 from /usr/include/sys/wait.h:43,
                 from /usr/include/stdlib.h:38,
                 from /opt/csw/include/c++/4.9.2/cstdlib:72,
                 from /opt/csw/include/c++/4.9.2/bits/stl_algo.h:59,
                 from /opt/csw/include/c++/4.9.2/algorithm:62,
                 from /mnt/software/solaris/wow/TrinityCore_3_3_5a/dep/cppformat/format.h:37,
                 from /mnt/software/solaris/wow/TrinityCore_3_3_5a/dep/cppformat/format.cc:28:
/mnt/software/solaris/wow/TrinityCore_3_3_5a/dep/cppformat/format.cc: In function ‘void {anonymous}::format_error_code(fmt::Writer&, int, fmt::StringRef)’:
/mnt/software/solaris/wow/TrinityCore_3_3_5a/dep/cppformat/format.cc:182:21: error: expected unqualified-id before numeric constant
   static const char ERR[] = "error ";
                     ^
compilation terminated due to -Wfatal-errors.
make[2]: *** [dep/cppformat/CMakeFiles/format.dir/format.cc.o] Error 1
make[1]: *** [dep/cppformat/CMakeFiles/format.dir/all] Error 2
make: *** [all] Error 2