Add userland test with mock kernel headers

contrib/linux-kernel/test/Makefile

@@ -0,0 +1,27 @@
+
+IFLAGS := -isystem include/ -I ../include/ -I ../lib/ -isystem googletest/googletest/include
+
+SOURCES := $(wildcard ../lib/*.c)
+OBJECTS := $(patsubst %.c,%.o,$(SOURCES))
+
+ARFLAGS := rcs
+CXXFLAGS += -std=c++11
+CFLAGS += -g -O0
+CPPFLAGS += $(IFLAGS)
+
+../lib/libzstd.a: $(OBJECTS)
+	$(AR) $(ARFLAGS) $@ $^
+
+UserlandTest: UserlandTest.cpp ../lib/libzstd.a
+	$(CXX) $(CXXFLAGS) $(CFLAGS) $(CPPFLAGS) $^ googletest/build/googlemock/gtest/libgtest.a googletest/build/googlemock/gtest/libgtest_main.a -o $@
+
+# Install googletest
+.PHONY: googletest
+googletest:
+	@$(RM) -rf googletest
+	@git clone https://github.com/google/googletest
+	@mkdir -p googletest/build
+	@cd googletest/build && cmake .. && $(MAKE)
+
+clean:
+	$(RM) -f *.{o,a} ../lib/*.{o,a}