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.
Previously, Linux-SGX logic of allocating/freeing enclave pages was
complicated and hard to read. This commit refactors this code for
readability, without changes in functionality.
borysp