minor, use trampoline and ucontext functions for slju coroutines

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
fix, PEBKAC, pass in arguments for next() directly (no static buffer in between)

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
chore, dispense with thread local variables

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, provide macro to detect whether asm backed coroutines would work

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, check for asm backed corus during configure and use them if available

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'core/coru-slju'

* core/coru-slju:
  minor, check for asm backed corus during configure and use them if available
  minor, provide macro to detect whether asm backed coroutines would work
  chore, dispense with thread local variables
  fix, PEBKAC, pass in arguments for next() directly (no static buffer in between)
  minor, use trampoline and ucontext functions for slju coroutines