This revision provides a choice to Linux users/distro maintainers: whilst we default to using the bundled source,If a user wishes to build `pyrogenesis` with support for Valgrind (such as it is), then can now do so by passing `--with-valgrind` to `update-workspaces.sh`. it is now possible to pass `--with-system-valgrind` to `update-workspaces.sh` and pull in the system-installed headers for `Valgrind` instead.(They will need Valgrind installed and locateable via `pkg-config`.)
Windows and OSX are unaffectedAccording to the Valgrind website, they don't - and probably never will - support Windows systems[1], so I've also made it non-Windows option.
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Since Alpha 16, Fedora has patched our `extern_libs.lua` file to use their repo-supplied `Valgrind` (to resolve https://bugzilla.redhat.com/show_bug.cgi?id=1141464). Now, they won't have to.
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[1] - https://valgrind.org/info/platforms.html, "Porting Plans"