A couple of minor fixes

1. Fixing ExceptionHandlerTest.FirstChanceHandlerRuns:
   exit() is not an async-signal-safe function (http://man7.org/linux/man-pages/man7/signal-safety.7.html)

2. Fixing entry point signature in minidump_dump
  Changed "const char* argv[]" to "char* argv[]" to match the standard entry point signature

3. Updating .gitignore to exclude unit test artifacts

Change-Id: I9662898d0bd97769621fb6476a720105821c60f0
Reviewed-on: https://chromium-review.googlesource.com/562356
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Ivan Penkov <ivanpe@chromium.org>
Reviewed-by: Joshua Peraza <jperaza@chromium.org>

src/client/linux/handler/exception_handler_unittest.cc

@@ -468,7 +468,7 @@ TEST(ExceptionHandlerTest, StackedHandlersUnhandledToBottom) {
 namespace {
 const int kSimpleFirstChanceReturnStatus = 42;
 bool SimpleFirstChanceHandler(int, void*, void*) {
-  exit(kSimpleFirstChanceReturnStatus);
+  _exit(kSimpleFirstChanceReturnStatus);
 }
 }