[automerger skipped] DO NOT MERGE: [libc++] Move __clamp_to_integral to <cmath>, and harden against min()/max() macros am: 7af7a63c2e am: d190f65c64 am: f0f107c222 -s ours am: b3d336063c -s ours
am: c940a9b998

Change-Id: Ibc6ef8eb7d2345f361ab2aad8aec5fd962e1861c