[RuntimeDyld] Don't try to allocate sections with align 0.

ELF sections allow 0 for the alignment, which is specified to
be the same as 1.  However many clients do not expect this and
will behave poorly in the presence of a 0-aligned section (for
example by trying to modulo something by the section alignment).
We can be more polite by making sure that we always pass a
non-zero value to clients.

Differential Revision: https://reviews.llvm.org/D57482

llvm-svn: 352694