Adds some error handling to the socket implementation.

runtime/bin/fdutils_macos.cc

Index: runtime/bin/fdutils_macos.cc
diff --git a/runtime/bin/fdutils_macos.cc b/runtime/bin/fdutils_macos.cc
index 25495daecf11f4966d07348efe9f14233b1496ff..ab1a603e91277fdcd66180bbeffb4f60cd5bf46c 100644
--- a/runtime/bin/fdutils_macos.cc
+++ b/runtime/bin/fdutils_macos.cc
@@ -21,10 +21,12 @@ bool FDUtils::SetCloseOnExec(intptr_t fd) {
   intptr_t status;
   status = NO_RETRY_EXPECTED(fcntl(fd, F_GETFD));
   if (status < 0) {
+    perror("fcntl(F_GETFD) failed");
     return false;
   }
   status |= FD_CLOEXEC;
   if (NO_RETRY_EXPECTED(fcntl(fd, F_SETFD, status)) < 0) {
+    perror("fcntl(F_SETFD, FD_CLOEXEC) failed");
     return false;
   }
   return true;
@@ -35,10 +37,12 @@ static bool SetBlockingHelper(intptr_t fd, bool blocking) {
   intptr_t status;
   status = NO_RETRY_EXPECTED(fcntl(fd, F_GETFL));
   if (status < 0) {
+    perror("fcntl(F_GETFL) failed");
     return false;
   }
   status = blocking ? (status & ~O_NONBLOCK) : (status | O_NONBLOCK);
   if (NO_RETRY_EXPECTED(fcntl(fd, F_SETFL, status)) < 0) {
+    perror("fcntl(F_SETFL, O_NONBLOCK) failed");
     return false;
   }
   return true;