[ELF] Use late evaluation for ALIGN in expression

While the following expression is handled fine:

  PROVIDE_HIDDEN(newsym = oldsym + address);

The following expression triggers an error because the expression
is evaluated as absolute:

  PROVIDE_HIDDEN(newsym = ALIGN(oldsym, CONSTANT(MAXPAGESIZE)) + address);

To avoid this error, we use late evaluation for ALIGN by making the
alignment an attribute of the expression itself.

Differential Revision: https://reviews.llvm.org/D33629

llvm-svn: 304185