configure.py/bootstrap.py uses CXX with CFLAGS

[geoff-nixon]

...rather than CXXFLAGS.
Thus,
CC=clang CXX=clang++ CFLAGS=-std=c11 CXXFLAGS=-std=c++11 configure.py; ninja
or the like raises
error: invalid argument '-std=c11' not allowed with 'C++/ObjC++'.

[nico]

ninja has no .c files. Is this really a problem?

[geoff-nixon]

Well, yes (IMHO). It doesn't particularly matter whether the project has .c or .cxx or .cpp or .cc files; it's that (by convention, I think? I actually can't seem to find any real citations or standards for this) typically flags for the C compiler are put in CFLAGS and flags for the C++ compiler are put in CXXFLAGS. The example I use above is a simplified one for demonstration; by default, the values I typically have exported are
-flto -fpic -fslp-vectorize-aggressive -march=native -Ofast -std=c11 in CFLAGS and
-flto -fpic -fno-asynchronous-unwind-tables -fslp-vectorize-aggressive -march=native -Ofast -std=c++11 -stdlib=libc++
in CXXFLAGS. Note that the error I report above only occurs because I have -std=c11 in my CFLAGS, which is probably rather rare; but a much more common occurrence, I think, is that the build will just ignore what one has set in CXXFLAGS and continue. This isn't ideal, however, since it will ignore pertinent settings like what type of exception handling info to generate and which C++ standard library against which I'd like to link. And as others have mentioned, building as C++11 often improves performance.

Now, of course, I'm sometimes a quick fellow, picked up on what was happening and set my CFLAGS to my CXXFLAGS for this project, but (again, only my opinion) one shouldn't have to do that, I don't think.

[geoff-nixon]

I'm closing the issue as I've opened #676 to address this.