Review all.sh for tests that use gcc or -O0 where they don't need to

[daverodgman]

Probably many tests still use gcc (as opposed to clang) or -O0 (or nothing specified, as opposed to -O2), where there is not a particular reason to do so. Review for tests where we can improve this. Tests where we actually run output built with -O0 will have the most impact.

[gilles-peskine-arm]

-O0

We only test with -O0 once per compiler (and not for all compilers).

nothing specified, as opposed to -O2

For make, the default is -Os. For CMake, the default is -O0, but it's -O2 with CMAKE_BUILD_TYPE=Release, -O3 with CMAKE_BUILD_TYPE=Asan and -Os with CMAKE_BUILD_TYPE=Check. We almost always pass a build type to CMake in all.sh but there are a few exceptions and it's Check in a couple of places.

For build-only components, we should use -O1. (-O0 is faster, but misses some static analysis that GCC or Clang can perform.)

Arguably -Os should not be the default. It's what a lot of our users want (in the microcontroller space), but those users typically pass -Os explicitly anyway, because they know they want to optimize for size. Linux distributions and such are more likely to use default settings and would be better served by -O2 or -O3. But that's a separate debate.