[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 skip reason: subject contains skip directive

Change-Id: I1123bb1c4d74301f0df1f55fc06f9eae614358bc