blit_executable(_int_flash) improvements

[Daft-Freak]

Basically this replaces blit_executable_int_flash(name crc.cpp) with blit_executable(name INTERNAL_FLASH src.cpp) but also:

• makes it work for external projects
• allows overriding the default with -DBLIT_EXECUTABLE_INTERNAL_FLASH=
• removes the sdl/pico stubs

(Somewhat inspired by add_executable(WIN32/MACOSX_BUNDLE) ... and needing a similar thing for pico standalone/loader builds)

[Gadgetoid]

oooh! Tidy! I guess there are precious few projects using this at all so it's a pretty safe merge?

[Daft-Freak]

If any, you'd have to manually pull in 32blit-stm32's CMakeLists to get _int_flash to work in an external project without this...

(Hmm, if anyone was doing that, it would probably still work as the function is still there...)

[Gadgetoid]

Boop beep I am ... not a bot :laughing:

Thank you!