Enable constant propagation for more math functions

Constant propagation for single precision math functions (such as
tanf) is already working, but was not enabled. This patch enables
these for many single-precision functions, and adds respective test
cases.

Newly handled functions: acosf asinf atanf atan2f ceilf coshf expf
exp2f fabsf floorf fmodf logf log10f powf sinhf tanf tanhf

llvm-svn: 246186