Allow InstAlias's to use immediate matcher patterns that xform the value.

Allow InstAlias's to use immediate matcher patterns that xform the value.

For example,

On ARM, "mov r3, #-3" is an alias for "mvn r3, #2", so we want to use a
matcher pattern that handles the bitwise negation when mapping to t2MVNi.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143233 91177308-0d34-0410-b5e6-96231b3b80d8