utests: fix bugs in builtin_tgamma().
utests: fix bugs in builtin_tgamma().

This patch is based on Rebecca's patch at:
 https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=5;filename=Fix-pow-erf-tgamma.patch;att=3;bug=768090.

And fixed another bug which we should not use an absolute error checking.
We should use ULP and considering the strict conformance or non strict
conformance state.

Signed-off-by: Zhigang Gong <e04a7b9b70b1e4c6318cf117dcd1a9056e14b97a@intel.com>
Signed-off-by: Rebecca Palmer <2decb937e7eca5e941ec22bc308fd452fe4ab2bb@zoho.com>
Reviewed-by: "Song, Ruiling" <286a174c1339c6eff91abc41c3a1012c95030c95@intel.com>

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