Avoid name clashes of builtins and runtime functions.

Avoid name clashes of builtins and runtime functions.

This makes it possible to use %Percent() notation to call any given builtin or runtime function in tests.

R=dslomov@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=21298

[Jakob Kummerow, 2014-05-12 13:32:33]

As discussed, I mostly resolved clashes by appending "JS" to the JavaScript
names involved in them. For three Math functions I made an exception and
appended "RT" to the runtime names instead, because those JavaScript identifiers
are used all over the compiler pipeline, so renaming those would have been much
more intrusive (and ugly: "case kMathExpJS" and such in
{H,L}UnaryMathInstruction). We can change the approach if you're not happy with
how this CL looks right now.

[Dmitry Lomov (no reviews), 2014-05-14 08:27:31]

lgtm

[Jakob Kummerow, 2014-05-14 08:51:28]

Committed patchset #1 manually as r21298 (presubmit successful).