[test] check strictest attributes possible for InferFunctionAttrs test

This appears to have all the same attributes as many other functions
in this file, and I think the use of INACCESSIBLEMEMONLY_NOFREE_NOUNWIND
instead of INACCESSIBLEMEMONLY_NOFREE_NOUNWIND_WILLRETURN was an
oversight that meant aligned_alloc's attributes were just going
unchecked. This patch corrects the test defect and now the attributes
inferred on aligned_alloc are actually validated, and the test still
passes.

Differential Revision: https://reviews.llvm.org/D117922