ptrace regression test fails to compile on arm64 platforms

While attempting to run the apparmor regression tests on on arm64 machine, the ptrace regression test fails to compile:

1166. cc -g -O0 -Wall -Wstrict-prototypes ptrace.c -lapparmor -o ptrace
1167. ptrace.c: In function ‘do_parent’:
1168. ptrace.c:40:14: error: storage size of ‘regs’ isn’t known
1169. struct user regs;
1170. ^
1171. ptrace.c:92:14: error: ‘PTRACE_GETREGS’ undeclared (first use in this function)
1172. if (ptrace(PTRACE_GETREGS, pid, NULL, ®s) == -1) {
1173. ^
1174. ptrace.c:92:14: note: each undeclared identifier is reported only once for each function it appears in
1175. ptrace.c:40:14: warning: unused variable ‘regs’ [-Wunused-variable]
1176. struct user regs;
1177. ^
1178. : recipe for target 'ptrace' failed
1179. make: *** [ptrace] Error 1

This is due to the arm64 platform only supporting the PTRACE_GETREGSET interface. As this interface is the preferred mechanism for getting access to arch-specific register information [0], the ptrace should be converted to using this by default.

[0] https://sourceware.org/ml/archer/2010-q3/msg00193.html