[msan] Use SIGHUP instead of SIGUSR1 in test.

Apparently, SIGUSR1 does not work on x86_64+ArchLinux for some reason.

For more details, see:
https://groups.google.com/forum/#!topic/llvm-dev/4Ag1FF4M2Dw

llvm-svn: 214289
diff --git a/compiler-rt/test/msan/chained_origin_with_signals.cc b/compiler-rt/test/msan/chained_origin_with_signals.cc
index ef98385..2841e34 100644
--- a/compiler-rt/test/msan/chained_origin_with_signals.cc
+++ b/compiler-rt/test/msan/chained_origin_with_signals.cc
@@ -25,9 +25,9 @@
   int volatile z;
   x = z;
 
-  signal(SIGUSR1, SignalHandler);
-  kill(getpid(), SIGUSR1);
-  signal(SIGUSR1, SIG_DFL);
+  signal(SIGHUP, SignalHandler);
+  kill(getpid(), SIGHUP);
+  signal(SIGHUP, SIG_DFL);
 
   return y;
 }