Include <linux/ptrace.h> regardless of <sys/reg.h> existence

This fixes compilation with musl libc.
This approach was already used in process.c, so I assume it is safe.

* signal.c: Move [HAVE_LINUX_PTRACE_H] code out of [HAVE_SYS_REG_H] check.
* syscall.c: Likewise.
* util.c: Likewise.

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
3 files changed