To be honest it took an incredible amount of time (to me) to enrich libposix enough for newlib to support GCC need.
Yet #Jehanne deviated from #Plan9 enough to make the port slightly simpler as Jehanne support ELF binaries while Plan 9 and #9front only run (custom) a.out binaries.
And to be honest, I have no idea on how to change the output binary format of GCC.