Graphene used its own implementations of memory-handling functions like
memcmp(), memcpy(), etc. These implementations were copied from Glibc
and contained complicated code from year 2004. Modern HW and compilers
do better job at optimizing simple C implementations of these functions.
Thus, this commit replaces old implementations with simple ones taken
from Musl libc and adapted to our code style.
One particular optimization is made to memcpy() on x86-64. memcpy() is
heavily used in Linux-SGX PAL to copy data in/out of SGX enclave.
Experiments with Redis 5.0 show perf improvement of using "rep movsb" at
3-5% for 4KB payloads over the previous implementation based on Glibc.
Plenty of bugfixes for Linux kernel later than 3.5 and Ubuntu later than 10.10.
More organized code to improve portability.
Regression tests for Pal to test completeness of implementation.
Michał Kowalczyk