Makefile: Add CPP code coverage

make/config.mk

@@ -47,6 +47,11 @@ LIB_RABIT = librabit.a
 # path to libjvm.so
 LIBJVM=$(JAVA_HOME)/jre/lib/amd64/server
 
+# whether to test with coverage measurement or not. (only used for `make cover`)
+# measured with gcov and html report generated with lcov if it is installed.
+# this disables optimization to ensure coverage information is correct
+TEST_COVER = 1
+
 # path to gtest library (only used when $BUILD_TEST=1)
 # there should be an include path in $GTEST_PATH/include and library in $GTEST_PATH/lib
 GTEST_PATH =