[analyzer] Use the common evalBind infrastructure for initializers.

This allows checkers (like the MallocChecker) to process the effects of the
bind. Previously, using a memory-allocating function (like strdup()) in an
initializer would result in a leak warning.

This does bend the expectations of checkBind a bit; since there is no
assignment expression, the statement being used is the initializer value.
In most cases this shouldn't matter because we'll use a PostInitializer
program point (rather than PostStmt) for any checker-generated nodes, though
we /will/ generate a PostStore node referencing the internal statement.
(In theory this could have funny effects if someone actually does an
assignment within an initializer; in practice, that seems like it would be
very rare.)

<rdar://problem/12171711>

llvm-svn: 162637