* tools: refactorize tools flags parsing.
Each SPIR-V tool was handing their own flag parsing. This PR
adds a new flag parsing utility that should be flexible enough
for our usage, but generic enough so it can be shared across tools while
remaining simple to use.
* cfg: replace cfg option parsing with the new one.
* change spirv-dis parsing + title + summary
* clang format
* flags: fix static init fiasco & remove help
Static initialization order is important, and was
working just by sheer luck.
Also removing the help generation tooling. It's less flexible than the
hand-written string, and making it as-good and as-flexible brings too
much complexity.
* review feedback
