Include intrin.h directly in Atomics.h instead of declaring functions manually from it

This is basically more of bug 1022049.

https://bugzilla.mozilla.org/show_bug.cgi?id=1025900
Include intrin.h in jemalloc.c

This fixes a linking error with clang-cl.
Replace some manual declarations of MSVC intrinsics with #include <intrin.h>