hwasan: refactor order of macros in hwasan_platform_interceptors.h [NFC]

Currently, the header file contains all the undefs, followed by all the
define X 0. This will be inconvenient for re-enabling interceptors,
because we would need to comment out (or delete) the corresponding macros
in two different places.

This patch groups together the macros for each function.

Additionally, it adds the suggestion that interceptors should be
re-enabled by commenting out (not deleting) the macros.

Differential Revision: https://reviews.llvm.org/D151371