For debugging, we are patching call sites to not call other
WASM_FUNCTIONs, but call WASM_TO_INTERPRETER stubs instead. When later
re-instantiating / cloning this code, the old logic for patching call
sites would miss those calls.
This CL changes the way we patch callsites by getting the called
function index per callsite from the bytecode. This requires iterating
both the source position table and the relocation table at the same
time to determine the byte position for each call.
Instead of looking up the functions to be replaced in a std::map, we now
get the function directly from a FixedArray. This reduces the complexity
from O(n*n*log(n)) to O(m), where n is the total number of functions and
m is the total byte code length (note that each function is patched
individually, so we set up the map n times before).
Constant factor are unclear though.

BUG=v8:5822
R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2627613002
Cr-Commit-Position: refs/heads/master@{#42259}