See also https://llvm.org/docs/GitBisecting.html for how to use git bisect run, which makes it possible to run the bisection completely automatically.
git bisect run
This is a great example of how being “clever” with macros in C can cause pain. The #x macro feature arguably breaks C since it allows tokens to be treated invisibly as a completely different kind of token.
In response to this, the macro was made less clever: https://pdfium.googlesource.com/pdfium/+/d539de991cacf02811880c434d4393c8275163d2