[libc++] Split off tests for aligned_alloc & friends into separate test files

This allows testing the rest of those headers on most platforms, instead
of XFAILing the whole test just because of a few functions.

As a fly-by fix, remove std/utilities/time/date.time/ctime.pass.cpp,
which was a duplicate of std/language.support/support.runtime/ctime.pass.cpp.

Differential Revision: https://reviews.llvm.org/D108295