llvm-link: Verify input modules

Otherwise, broken input modules can cause assertions.  I've updated two
of the testcases that started failing (modules that had `Require` flags
but didn't meet their own requirements), but Rafael and I decided that
test/Linker/2011-08-22-ResolveAlias.ll should just be deleted outright
-- it's a leftover of the way llvm-gcc used to implement weakref.

llvm-svn: 233229