[libc] Add hardware implementations of ceil and ceilf for aarch64.

This change also introduces a new source layout for adding machine
specific and generic implementations. To keep the scope of this change
small, this new pattern is only applied for ceil, ceilf and ceill.
Follow up changes will switch all math functions in to the new pattern.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D95850