osutil: allow disabling setprocname via a define passed to the compiler In some situations, we run a custom python launcher that appears to not set up Py_GetArgcArgv correctly. We then proceed to promptly crash when we attempt to dereference NULL. Being able to completely disable setprocname is beneficial in these situations, since we won't even attempt to use it, even if the case that causes the crash is fixed. Right now, if I compile osutil.so with -DSETPROCNAME_USE_NONE, the compilation fails on python3 due to SETPROCNAME_USE_NONE redefinition. I could possibly work around that, but it's likely helpful to have a way of disabling this completely without it being brittle (i.e. if python3 ever gains the ability to perform this operation). Differential Revision: https://phab.mercurial-scm.org/D6865