Support running just the GEMV version of the thread safety test

Author: martin-frbg

Makefile

@@ -146,6 +146,9 @@ ifneq ($(NO_CBLAS), 1)
 ifeq ($(CPP_THREAD_SAFETY_TEST), 1)
 	$(MAKE) -C cpp_thread_test all
 endif
+ifeq ($(CPP_THREAD_SAFETY_GEMV), 1)
+	$(MAKE) -C cpp_thread_test dgemv_tester
+endif
 endif
 endif