linux-user: Split strace prototypes into strace.h

linux-user: Split strace prototypes into strace.h

The functions implemented in strace.c are only used in a few files in
linux-user; split them out of qemu.h and into a new strace.h header
which we include in the places that need it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210908154405.15417-3-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>