fix builtin function "fract"
fix builtin function "fract"

v2: return nan for nan, +zero for +inf, -zero for -inf.
Signed-off-by: Homer Hsing <f17cb7083eb6a94c3fb9d8f09ceefa518f721ab2@intel.com>
Reviewed-by: "Yang, Rong R" <78759e37dc7114caed18f74e7515c5cb519dbf6d@intel.com>

ignatenkobrain/beignet,freedesktop-unofficial-mirror/beignet,zhenyw/beignet,wdv4758h/beignet,wdv4758h/beignet,freedesktop-unofficial-mirror/beignet,wdv4758h/beignet,ignatenkobrain/beignet,freedesktop-unofficial-mirror/beignet,ignatenkobrain/beignet,zhenyw/beignet,wdv4758h/beignet,zhenyw/beignet,zhenyw/beignet,zhenyw/beignet,wdv4758h/beignet,freedesktop-unofficial-mirror/beignet,ignatenkobrain/beignet,ignatenkobrain/beignet