fix coverage build

Author: igagis

config/gcov.mk

@@ -0,0 +1,11 @@
+include $(config_dir)base/base.mk
+
+# no optimization to avoid mismamtch of actual code to source lines,
+# otherwise coverage report will not be accurate
+this_cxxflags += -O0
+
+this_cxxflags += -ftest-coverage
+this_cxxflags += -fprofile-arcs
+this_cxxflags += --coverage
+
+this_ldflags += --coverage