[AArch64] Enable libm vectorized functions via SLEEF

It enables trigonometry functions vectorization via SLEEF: http://sleef.org/.

  - A new vectorization library enum is added to TargetLibraryInfo.h: SLEEF.
  - A new option is added to TargetLibraryInfoImpl - ClVectorLibrary: SLEEF.
  - A comprehensive test case is included in this changeset.
  - A new vectorization library argument is added to -fveclib: -fveclib=SLEEF.

Trigonometry functions that are vectorized by sleef:
acos
asin
atan
atanh
cos
cosh
exp
exp2
exp10
lgamma
log10
log2
log
sin
sinh
sqrt
tan
tanh
tgamma

Co-authored-by: Stefan Teleman

Reviewed By: paulwalker-arm

Differential Revision: https://reviews.llvm.org/D134719