Add missing test/gtest.mk script.

test/gtest.mk

@@ -0,0 +1,21 @@
+# gtest.mk
+# Uses the source code version of GoogleTest, assumed to be installed at /usr/src/gtest.
+GTEST_PATH ?= /usr/src/gtest
+GTEST_OBJS = gtest-all.o
+LDLIBS += -lpthread
+LDLIBS += -lstdc++
+vpath %.cc $(GTEST_PATH)/src
+
+GTEST_FOUND = $(ls -d $(GTEST_PATH)/src/main.cc)
+ifeq (,$(GTEST_FOUND))
+  $(info )
+  $(info Error:)
+  $(info GoogleTest sources were not found at the path:)
+  $(info GTEST_PATH=$(GTEST_PATH))
+  $(info Suggested corrective action: sudo apt-get install libgtest-dev)
+  $(info )
+  $(error Please setup GTEST_PATH so that gtest-all.cc can be found.)
+endif
+
+all:
+gtest-all.o: CXXFLAGS += -I$(GTEST_PATH)