[automerger skipped] DO NOT MERGE: [libc++] Add `__truncating_cast` for safely casting float types to integers am: 55b6136b3a am: 9546d85a3d am: c3a80bd37a -s ours am: f126b4ea11 -s ours am: 9432e1044b am: f4f52f6f73 am: 367fe25436
am: f9a1a6da7f -s ours
am skip reason: subject contains skip directive

Change-Id: I0e3ccb79a6d258bfbc631f341cdbc9c4c8fda728