Esp-idf has an improved but still kind of abused cmake-
based build system now.
If we see ESP_PLATFORM coming as a cmake var, we can know we
are being built from inside the esp-idf config system.
Leave the existing esp32 arrangements alone but triggered off
ESP_PLATFORM, adapt to use the cross toolchain file and
various quirks automatically.
In this way you can build lws a part of your project in a
much cleaner way.
Prepare a minimal esp32 test app for use in Sai
Adapt .sai.json to build for esp32
The cmake config on the build system actually decides the release build optimization policy.
On Fedora, it's -O2. On Ubuntu, it's -O3.
Anything given in CMakeLists.txt is overridden by the build system policy since it goes at
the end of the compiler commandline.
When you are building cross, the build system's opinion of your cross binary optimization
level is irrelevant, and at worst destructive. Some versions of gcc contain broken optimizations
that are applied only at -O3.
This patch removes any doomed attempt to set -O in CMakeLists.txt, which has
no effect since the build system policy is still added at the end, but
removes confusion; and adds code to all the cross build files to forcibly
override release optimization level to -O2, removing the build system's
opinion of how your cross build should look.
