unstarted_runtime: add cutout for Math.floor

Needed in order to make BouncyCastleProvider initializable in
compile time

(cherry picked from commit a8908ef14cf2d2e0d05e41e319da5d6909325ae2)
Bug: 28108158

Change-Id: Id6b4e3d4dde45354562603f41134d8d21da2b423
2 files changed