The arithmetic within the loop was not adjusted properly after SIGRTMIN
was stolen for the guest SIGABRT.  The effect was that the guest libc
could not send itself __SIGRTMIN to wake sleeping threads.

Fixes: 38ee0a7d ("linux-user: Remap guest SIGABRT")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1967


Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>