[APInt] Use trailing bit counting methods instead of population count method in isAll...

[APInt] Use trailing bit counting methods instead of population count method in isAllOnesValue, isMaxSigendValue, and isMinSignedValue. NFCI

The trailing bit methods will early out if they find a bit of the opposite while popcount must always look at all bits. I also assume that more CPUs implement trailing bit counting with native instructions than population count.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306154 91177308-0d34-0410-b5e6-96231b3b80d8