riscv-gcc-prebuilt: add builded commit hash to doc

[andkae]

Hi Stephan,

your Prebuilt GCC is a real big deal. It makes the compile of source code easily. But whenever you are in need to build your GCC from scratch it would be very helpful to store also the used commit for build in your table:

This table could for instance modified to:

Status	Release (tag)	Download	GCC	binutils	march	mabi	c-lib
🔴	rv32i-4.0.0	💾 download	12.1.0	2.39	rv32i	ilp32	newlib

Could this suitable?

Thanks and BR,
Andreas

[stnolting]

Great idea! Let's keep this open until the next toolchain upload.