Create a new linker section .unitialized_bss for bss that does not need
zero-initialising.
Move gc_heap to this section, which saves ~30ms from rising edge of RESET
to setting a pin HIGH in MicroPython.
Zero fill happens in Pico SDK crt0.S before ROSC is configured. It's very,
very slow.
Signed-off-by: Phil Howard <phil@gadgetoid.com>
71f6eb5ac9