This is the first step in removing this obsolete header.
Additionally, AtomicMath test is removed, as it became obsolete after
these changes (and was relying on undefined behaviors anyway).
Sometimes we need to prevent the compiler from reading or writing to
a memory location twice to prevent certain TOCTOU bugs. This can now
be achieved by using the introduced macros and this commit does so in
enclave_ocalls.c for Linux-SGX.