> how cross compiler generate 36-bit code on 32-bit machine?

Same way any foreign code is generated - mostly up to the assembler and
linker.  Define a way of representing 36-bit words (as, say, 5 8-bit
bytes with 4 bits wasted, or two 36-bit words in 9 8-bit bytes, or even
in extremis one 36-bit word stored in a 64-bit space with 28 bits of
padding).  Setting up the first boot may be a bit interesting,
depending on the boot methods and media, but that's about it.

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