Documentation for TARGETS variable was added
One more example for using TARGETS variable.
TARGETS variable is now exported for subprojects.
Add missing test.mk for examples/hello_TARGETS
Minor code clean-ups
Introduction of CFLAGS.dflt.${CC_TYPE} and CXXFLAGS.dflt.${CXX_TYPE}.
-Qunused-arguments is always used for clang and clang++.
virtual subprojects: existence of subdir/Makefile is checked.
mkc.minitest.mk: new variable TEST_PREREQS
mkc.configure.mk: negative results for MKC_REQUIRE_* are not cached.
This gives users ability to fix the problem by changing the environment.
fix for tests/reqd_clean_cache