raise SystemExit on build failure

[rgommers]

Good idea from @henryiii in #222 (comment): When Meson fails, we should raise SystemExit (like setuptools usually does), not throw an exception. Pip/build report a mess when there's an uncaught exception from the build hooks, while SystemExit is handled gracefully without nearly as many extra reports about missing build hooks and changed exceptions. The actual failure is printed by Meson.