sim: Suppress non-literal printf warning

sim: Suppress non-literal printf warning

Clang generates a warning if the format string of a printf-like function is
not a literal ("-Wformat-nonliteral"). On the default configuration, it
causes a build failure (unless "--disable-werror" is specified).

To avoid this warning, this commit now uses vsnprintf to format error
message and pass the message to sim_engine_abort function with another
printf-style formatting.

This patch is mostly authored by Andrew Burgess and slightly modified by
Tsukasa OI.

Co-authored-by: Andrew Burgess <aburgess@redhat.com>
Signed-off-by: Tsukasa OI <research_trasio@irq.a4lg.com>