Split CPPFLAGS and CFLAGS more carefully This has no change to the build, but makes it easier to try other build tools that only want CPPFLAGS

attrs==21.2.0
iniconfig==1.1.1
packaging==21.0
pluggy==1.0.0
py==1.10.0
pyparsing==2.4.7
pytest==6.2.5
toml==0.10.2
psutil==5.9.0