Add the following functions:

- SYSCALL (normal fast system call instruction) [0f 05]
- SYSENTER (system call entry instruction) [0f 34]
- SYSEXIT (system call exit instruction) [0f 35]
- SYSEXIT64 (system call exit instruction to 64-bit user code) [REX.W 0f 35]
- SYSRET (system call return instruction) [0f 07]

Patch by Sean Callanan.

llvm-svn: 76528