RFC: Build: Add support for generating cflow reports for cmdline tools.

[clumens]

cflow is a program that generates reports of function call chains in C source files. I find it most useful in determining where a function I want to get rid of is getting called, though it could be used for a bunch of other things.

It's really most useful if you give it a function. Otherwise, it will generate all possible call chains, which is very large. Pass the function you're interested in (and any other extra arguments) via the CFLOW_FLAGS environment variable.

For instance, if you want to see everwhere that calls crm_perror:

$ make -C tools CFLOW_FLAGS="--target crm_perror" cflow

Or, you can see everything that a single function calls:

$ make -C tools CFLOW_FLAGS="--main pcmk__add_mainloop_ipc" cflow

However note that in this case, the per-tool output makes less sense. You'll probably just end up with a bunch of duplicate copies of a single report.

Additionally, if you're only interested in generating a report for a single command line tool, you can do this:

$ make -C tools CFLOW_FLAGS="--target crm_perror" crm_rule.cflow

Other things to note:

• You do not need to build the source before running this.

• It will output a lot of warnings about redefinitions, which I think is mostly due to reusing argument names and things like that. It doesn't seem to be causing problems.

• I have purposefully not added any -Idir include arguments to the call to cflow. It will take these, but it doesn't seem to do much for us at the moment besides slow everything way down.