Replaced signbit(int64_t x) with x & INT64_MIN.
Replaced signbit(int64_t x) with x & INT64_MIN.

bitfusionio/Oclgrind,mpflanzer/Oclgrind,surround-io/oclgrind,surround-io/oclgrind,surround-io/oclgrind,bitfusionio/Oclgrind,mpflanzer/Oclgrind,surround-io/oclgrind,mpflanzer/Oclgrind,bitfusionio/Oclgrind,bitfusionio/Oclgrind,mpflanzer/Oclgrind