[DeveloperPolicy] Changes should not caused major compile-time regressions

[nikic]

Summary

Document that changes should not cause major correctness, performance or compile-time regressions. In line with the previous wording, this is kept vague and what constitutes a "major" regression is left up to case-by-case evaluation.

llvm/docs/DeveloperPolicy.rst

#. The code must not cause regressions on a reasonable subset of llvm-test,
    might be something like "``llvm-test/MultiSource/Benchmarks``".
 
 Additionally, the committer is responsible for addressing any problems found in
 the future that the change is responsible for.  For example:
 
 * The code should compile cleanly on all supported platforms.
 
 * The changes should not cause any correctness regressions in the ``llvm-test``
-  suite and must not cause any major performance regressions.
+  suite and must not cause any major performance or compile-time regressions.
 
 * The change set should not cause performance or correctness regressions for the
   LLVM tools.
 
 * The changes should not cause performance or correctness regressions in code
   compiled by LLVM on all applicable targets.
 
 * You are expected to address any `Bugzilla bugs <https://bugs.llvm.org/>`_ that