math: Use precomputed constant for log2(10.0)

exp10 CTS fails with or without this change

Reviewer: Jeroen Ketema
Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>

git-svn-id: https://llvm.org/svn/llvm-project/libclc/trunk@318063 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed