Legacy Makefiles: Don't force C++14 with GCC 4.8.

Bug 200618218

Author: brycelelbach

Makefile

@@ -14,8 +14,8 @@
 
 # Makefile for building Thrust unit test driver
 
-# Force C++14 mode. NVCC will ignore it if the host compiler doesn't support it.
-export CXX_STD := c++14
+# Force C++11 mode. NVCC will ignore it if the host compiler doesn't support it.
+export CXX_STD := c++11
 
 export CCCL_ENABLE_DEPRECATIONS := 1