riscv: support large stack and far jumps
riscv: support large stack and far jumps

for 101_cleanup we need 256kb stack (with the associated problem
of needing a larger prologue/epilogue) as well as jumps out of
range for the 21bit offsets (exactly for second part of the prologue).

mingodad/tinycc,mirror/tinycc,mingodad/tinycc,mirror/tinycc,mingodad/tinycc,mirror/tinycc,mirror/tinycc,mingodad/tinycc