The typical pattern for using BuildCCall was to create a stack-allocated array
of arguments, which was passed to BuildCCall. BuildCCall then would allocate
scratch space using WasmGraphBuilder::Buffer and copy the arguments into the
scratch space. This copy is unnecessary and also the use of Buffer can lead to
silently overwriting scratch space that may be used higher up the stack.

Now BuildCCall takes all of the functions parameters as arguments and stores
this directly in a stack-allocated buffer, avoiding the use of Buffer at all and
all its associated pitfalls.

Change-Id: Ia0de9a90350d7fcbbb1b05d28e735d790a5f9143
Reviewed-on: https://chromium-review.googlesource.com/701638Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Eric Holk <eholk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48350}