- `-fomit-frame-pointer` is included automatically by both GCC and
Clang in `-O1` and above.
- `-ftree-vectorize` is included automatically by GCC in `-O2` and
beyond, and seems always enabled by Clang.
Closes#66296. See that issue for a detailed investigation.
Adds support for LTO on macOS and Android. We don't have much experience
with LTO on these platforms so for now we keep it disabled by default
even when `production=yes` is set.
Similarly for iOS where we ship object files for the user to link in
Xcode so LTO makes builds extremely slow to link.
`production=yes` defaults to full LTO.
ThinLTO is much faster for LLVM-based compilers but seems to produce
bigger binaries (at least for the Web platform).
