linux/android: add SIGTRAP to the list of signals handled by the client

__builtin_trap() causes a SIGTRAP on arm64 (at least with GCC 4.9).
SIGTRAP is not handled by breakpad, causing crashes induced by
__builtin_trap() to be missed.
Note that on x86 and arm, instead, __builtin_trap() raises a SIGILL,
which is already handled by breakapd.

BUG=chromium:614865
[email protected]

Review URL: https://codereview.chromium.org/2042853002 .

Author: primiano

src/client/linux/handler/exception_handler.cc

@@ -118,7 +118,7 @@ namespace {
 // all these signals must be Core (see man 7 signal) because we rethrow the
 // signal after handling it and expect that it'll be fatal.
 const int kExceptionSignals[] = {
-  SIGSEGV, SIGABRT, SIGFPE, SIGILL, SIGBUS
+  SIGSEGV, SIGABRT, SIGFPE, SIGILL, SIGBUS, SIGTRAP
 };
 const int kNumHandledSignals =
     sizeof(kExceptionSignals) / sizeof(kExceptionSignals[0]);