When compiling a library that contains both C and C++ files, we commonly need to set both CFLAGS and CXXFLAGS, often to the same value, or at least with a large common denominator.

We should have a separate value that means "this goes to both the C and the C++ compiler", and then use CFLAGS and CXXFLAGS only for those flags that need to go to only one of the compilers, but not both.

We have been discussing this for a long time, but had a hard time finding a good name for this set of common or shared C/C++ flags. A good name should be clear, unambiguous and not unwieldy. Most ideas we had failed on one or more of these accounts.

The current suggestion is to use CFAMILYFLAGS. We believe this fulfills the requirements.

This bug relates to JDK-8001877, but that is almost an umbrella bug dealing with additional issues we have with our CFLAGS/CXXFLAG handling, so I created this issue to clearly separate just the part about joining duplicated flags.