Do not include sys/ptrace.h and sys/user.h unconditionally.
Other portability fixes.

include/config.h.in

diff --git a/include/config.h.in b/include/config.h.in
index 0481da9..8d690e4 100644
--- a/include/config.h.in
+++ b/include/config.h.in
@@ -401,6 +401,9 @@
 /* Define if you have the <sys/param.h> header file.  */
 #undef HAVE_SYS_PARAM_H
 
+/* Define if you have the <sys/ptrace.h> header file.  */
+#undef HAVE_SYS_PTRACE_H
+
 /* Define if you have the <sys/reg.h> header file.  */
 #undef HAVE_SYS_REG_H
 
@@ -428,6 +431,9 @@
 /* Define if you have the <sys/syscall.h> header file.  */
 #undef HAVE_SYS_SYSCALL_H
 
+/* Define if you have the <sys/user.h> header file.  */
+#undef HAVE_SYS_USER_H
+
 /* Define if you have the <sys/v86.h> header file.  */
 #undef HAVE_SYS_V86_H