This patch is large, but is almost entirely just adding casts to calls
to syscall_impl. Much of the work was done programatically, with human
checking when the syntax or types got confusing.
Reviewed By: mcgrathr
Differential Revision: https://reviews.llvm.org/D156950
Add the syscall wrapper function and tests. It's implemented using a
macro to guarantee the minimum number of arguments.
Reviewed By: sivachandra, lntue
Differential Revision: https://reviews.llvm.org/D134919