Consistently check 'IsCode' when allocating sections in RuntimeDyld (via

findOrEmitSection).

Vaidas Gasiunas's patch, r201259, fixed one instance where we were always
allocating sections as text. This patch fixes the remaining buggy call sites.

No test case: This isn't breaking anything that I know of, it's just
inconsistent.

<rdar://problem/15943542>

llvm-svn: 201605