Print more debug info on semaphore failure.

src/base/platform/semaphore.cc

Index: src/base/platform/semaphore.cc
diff --git a/src/base/platform/semaphore.cc b/src/base/platform/semaphore.cc
index f53df6741f56a62c991c560ae68a4289bbe74601..6225b1655f881fe4fe3ff47f8c1912d9d5995181 100644
--- a/src/base/platform/semaphore.cc
+++ b/src/base/platform/semaphore.cc
@@ -101,7 +101,9 @@ Semaphore::~Semaphore() {
 
 void Semaphore::Signal() {
   int result = sem_post(&native_handle_);
-  CHECK_EQ(0, result);
+  if (result != 0) {
+    V8_Fatal(__FILE__, __LINE__, "Semaphore signal failure: %d\n", errno);
+  }
 }