Fix an issue where we were reusing materializations of constants in blocks not...

Fix an issue where we were reusing materializations of constants in blocks not dominated by the materialization.  This is
the simple fix, materializing the constant before every use.  It might be better to either track domination of uses or
to materialize all constants and the beginning of the function and let remat sort when to do materialization at uses.

llvm-svn: 55703