Consider (x == -1) unlikely in BranchProbabilityInfo

This adds another heuristic to BPI, similar to the existing heuristic that
considers (x == 0) unlikely to be true. As suggested in the PACT'98 paper by
Deitrich, Cheng, and Hwu, -1 is often used to indicate an invalid index, and
equality comparisons with -1 are also unlikely to succeed. Local
experimentation supports this hypothesis: This yields a 1-2% speedup in the
test-suite sqlite benchmark on the PPC A2 core, with no significant
regressions.
[ARM] Fix Tag_ABI_HardFP_use build attribute

Fix Tag_ABI_HardFP_use build attribute to handle single precision FP,
replace deprecated Tag_ABI_HardFP_use value of 3 with 0 and also add
some tests for Tag_ABI_VFP_args.
Sema: Make helper function static.