[PATCH -next] c6x: fix build of signal.c using _TIF_SIGNALs

[Randy Dunlap]

kernel/signal.c in arch/c6x/ needs <asm/asm-offsets.h> to build
since it contains _TIF_SIGNALfoobar #defines, so add it.

Placates these build errors:

../arch/c6x/kernel/signal.c: In function 'do_notify_resume':
../arch/c6x/kernel/signal.c:316:27: error: '_TIF_SIGPENDING' undeclared (first use in this function); did you mean 'TIF_SIGPENDING'?
  316 |  if (thread_info_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
      |                           ^~~~~~~~~~~~~~~
../arch/c6x/kernel/signal.c:316:27: note: each undeclared identifier is reported only once for each function it appears in
../arch/c6x/kernel/signal.c:316:45: error: '_TIF_NOTIFY_SIGNAL' undeclared (first use in this function); did you mean 'TIF_NOTIFY_SIGNAL'?
  316 |  if (thread_info_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
      |                                             ^~~~~~~~~~~~~~~~~~

Fixes: b7560cfc3f8a ("c6x: add support for TIF_NOTIFY_SIGNAL")
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: linux-c6x-dev@xxxxxxxxxxxxx
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Mark Salter <msalter@xxxxxxxxxx>
Cc: Aurelien Jacquiot <jacquiot.aurelien@xxxxxxxxx>
---
 arch/c6x/kernel/signal.c |    1 +
 1 file changed, 1 insertion(+)

--- linux-next-20201209.orig/arch/c6x/kernel/signal.c
+++ linux-next-20201209/arch/c6x/kernel/signal.c
@@ -13,6 +13,7 @@
 #include <linux/syscalls.h>
 #include <linux/tracehook.h>
 
+#include <asm/asm-offsets.h>
 #include <asm/ucontext.h>
 #include <asm/cacheflush.h>