By disabling C++ optimizations for code that's only run in mksnapshot,
that is, CSA and Torque-generated code, we can save compile time.
I observed up to 2x improvements of compile time for some files,
while the mksnapshot time did not increase significantly.

Bug: v8:7629
Change-Id: I96be2966611b2471b68023e0dd9e351d94f0013c
Reviewed-on: https://chromium-review.googlesource.com/c/1460941Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59585}