Import base::ieee754::exp() from FreeBSD msun and introduce a Float64Exp
TurboFan operator based on that, similar to what we do for Float64Log.
Rewrite Math.exp() as TurboFan builtin and use that operator to also
inline Math.exp() into optimized TurboFan functions.

CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel
BUG=v8:3266,v8:3468,v8:3493,v8:5086,v8:5108,chromium:620786
R=mvstanton@chromium.org

Committed: https://crrev.com/93e26314afc9da9b5b8bd998688262444ed73260
Review-Url: https://codereview.chromium.org/2077533002
Cr-Original-Commit-Position: refs/heads/master@{#37037}
Cr-Commit-Position: refs/heads/master@{#37047}