[Beignet] how about we remove the -ffast-math compiler flag

[Lu, Guanqun]

Hi list,

as our cl runtime doesn't take lots of math heavy computation, how about we release the contraints of using fast-math for our compiler, when I'm compiling beignet using gcc 4.7.3, it has the following errors:

Scanning dependencies of target gbe
[  1%] Building CXX object backend/src/CMakeFiles/gbe.dir/ocl_stdlib_str.cpp.o
[  1%] Building CXX object backend/src/CMakeFiles/gbe.dir/ocl_common_defines_str.cpp.o
[  2%] Building CXX object backend/src/CMakeFiles/gbe.dir/sys/intrusive_list.cpp.o
In file included from /usr/include/math.h:423:0,
                 from /usr/lib/gcc/i686-pc-linux-gnu/4.7.3/../../../../include/c++/4.7.3/cmath:46,
                 from /usr/lib/gcc/i686-pc-linux-gnu/4.7.3/../../../../include/c++/4.7.3/random:38,
                 from /usr/lib/gcc/i686-pc-linux-gnu/4.7.3/../../../../include/c++/4.7.3/bits/stl_algo.h:67,
                 from /usr/lib/gcc/i686-pc-linux-gnu/4.7.3/../../../../include/c++/4.7.3/algorithm:63,
                 from /root/beignet/backend/src/./sys/alloc.hpp:29,
                 from /root/beignet/backend/src/./sys/platform.hpp:345,
                 from /root/beignet/backend/src/sys/intrusive_list.hpp:26,
                 from /root/beignet/backend/src/sys/intrusive_list.cpp:23:
/usr/include/bits/math-finite.h:25:53: error: declaration of 'double acos(double)' has a different exception specifier
In file included from /usr/include/math.h:71:0,
                 from /usr/lib/gcc/i686-pc-linux-gnu/4.7.3/../../../../include/c++/4.7.3/cmath:46,
                 from /usr/lib/gcc/i686-pc-linux-gnu/4.7.3/../../../../include/c++/4.7.3/random:38,
                 from /usr/lib/gcc/i686-pc-linux-gnu/4.7.3/../../../../include/c++/4.7.3/bits/stl_algo.h:67,
                 from /usr/lib/gcc/i686-pc-linux-gnu/4.7.3/../../../../include/c++/4.7.3/algorithm:63,

But removing the -ffast-math solves the issue.

If you think this is a good idea, I can send out a simple patch.

Thanks!
--guanqun