In semihosting mode QEMU allows guest to read and write host file
descriptors directly, including descriptors 0..2, a.k.a. stdin, stdout
and stderr. Sometimes it's desirable to have semihosting console
controlled by -serial option, e.g. to connect it to network.
Add semihosting console to xtensa-semi.c, open it in the 'sim' machine
in the presence of -serial option and direct stdout and stderr to it
when it's present.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
8128b3e079