THRIFT-3608 lib/cpp/test/SecurityTest is flaky in jenkins Thrift-precommit build.
Client: Test (C++)
Patch: John Sirois

Previously, the deprecated `linux` symbol was tested, but under both g++
and clang++ using `-std=c++11` this deprecated symbol is not defined.
Test the accepted modern standard of `__linux__` instead to ensure the
SIGPIPE ignore is in-effect and the test runs stably.

This closes #848
diff --git a/lib/cpp/test/SecurityTest.cpp b/lib/cpp/test/SecurityTest.cpp
index 1369077..5e9dfe4 100644
--- a/lib/cpp/test/SecurityTest.cpp
+++ b/lib/cpp/test/SecurityTest.cpp
@@ -31,7 +31,7 @@
 #include <thrift/transport/TTransport.h>
 #include "TestPortFixture.h"
 #include <vector>
-#ifdef linux
+#ifdef __linux__
 #include <signal.h>
 #endif
 
@@ -60,7 +60,7 @@
 			BOOST_TEST_MESSAGE(boost::format("argv[%1%] = \"%2%\"") % i % master_test_suite().argv[i]);
 		}
 
-    #ifdef linux
+    #ifdef __linux__
 		// OpenSSL calls send() without MSG_NOSIGPIPE so writing to a socket that has
 		// disconnected can cause a SIGPIPE signal...
 		signal(SIGPIPE, SIG_IGN);
@@ -83,7 +83,7 @@
     virtual ~GlobalFixture()
     {
 		apache::thrift::transport::cleanupOpenSSL();
-#ifdef linux
+#ifdef __linux__
 		signal(SIGPIPE, SIG_DFL);
 #endif
     }