upgrading to google benchmark v1.5.1; modifying with new version number

Author: syclik

make/libraries

@@ -7,7 +7,7 @@ EIGEN ?= $(MATH)lib/eigen_3.3.7
 OPENCL ?= $(MATH)lib/opencl_2.2.0
 TBB ?= $(MATH)lib/tbb_2019_U8
 SUNDIALS ?= $(MATH)lib/sundials_5.2.0
-BENCHMARK ?= $(MATH)lib/benchmark_
+BENCHMARK ?= $(MATH)lib/benchmark_1.5.1
 GTEST ?= $(BENCHMARK)/googletest/googletest
 CPPLINT ?= $(MATH)lib/cpplint_1.4.5