[ELF] - Implemented linkerscript ALIGN command

ALIGN(exp)
Return the location counter (.) aligned to the next exp boundary. (https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/4/html/Using_ld_the_GNU_Linker/expressions.html)

Patch implements this command.
This fixes PR27406.

Differential revision: http://reviews.llvm.org/D19364

llvm-svn: 267145