user/spice-gtk: switch coroutine impl from ucontext to gthread
Fixes a failure on ppc32:
8/12 spice-gtk / test-coroutine FAIL 0.02 s (killed by signal 6 SIGABRT)
--- command ---
/usr/src/packages/user/spice-gtk/src/spice-gtk-0.38/output/tests/test-coroutine
--- stdout ---
# random seed: R02S414e77a117fac2e9cd10eee9a9f61d84
1..3
# Start of coroutine tests
Bail out! GSpice:ERROR:../tests/coroutine.c:37:test_coroutine_simple: assertion failed (GPOINTER_TO_INT(result) == 0x42): (0 == 66)
--- stderr ---
**
GSpice:ERROR:../tests/coroutine.c:37:test_coroutine_simple: assertion failed (GPOINTER_TO_INT(result) == 0x42): (0 == 66)
-------
Edited by Max Rees