gcc -O1 and async/thread

[wluker]

The async/thread example at https://github.com/ceu-lang/ceu/blob/master/samples/test-03.ceu works with default compiler settings, but doesn't work when optimization is turned on -O1.

CEU_SRC=./samples/test-03.ceu CEU_ARGS="--ceu-features-async=true --ceu-features-thread=true --ceu-features-dynamic=true" CC_ARGS="-O0" make one

/tmp/test-03 works as expected, but change -O0 to -O1 and ceu starts the thread, but the main ceu loop then blocks