[ELF] - Check that section alignment is a power of 2.

I found that this check still may be useful in some cases.
At fact since we use uint32_t alignment, then maximum value
that is valid for us is 0x80000000. But some broken files,
for example file from testcase may have greater value.
Because of that offset calculation overflow and crash happens.

Differential revision: https://reviews.llvm.org/D25324

llvm-svn: 283544