um: Compile with modern headers

Recent libcs have gotten a bit more strict, so we actually need to
include the right headers and use the right types. This enables UML to
compile again.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: stable@vger.kernel.org
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/os-Linux/file.c

@@ -12,6 +12,7 @@
 #include <sys/mount.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
+#include <sys/sysmacros.h>
 #include <sys/un.h>
 #include <sys/types.h>
 #include <os.h>

arch/um/os-Linux/signal.c

@@ -16,6 +16,7 @@
 #include <os.h>
 #include <sysdep/mcontext.h>
 #include <um_malloc.h>
+#include <sys/ucontext.h>
 
 void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
 	[SIGTRAP]	= relay_signal,

arch/x86/um/stub_segv.c

@@ -6,6 +6,7 @@
 #include <sysdep/stub.h>
 #include <sysdep/faultinfo.h>
 #include <sysdep/mcontext.h>
+#include <sys/ucontext.h>
 
 void __attribute__ ((__section__ (".__syscall_stub")))
 stub_segv_handler(int sig, siginfo_t *info, void *p)