kvm: testsuite: silence warnings on x86_64

kvm: testsuite: silence warnings on x86_64

This patch fixes user/test/x86/emulator.flat on kvm-59 with x86_64/E6850
and three other warnings:

test/x86/access.c: In function 'ac_test_exec':
test/x86/access.c:541: warning: implicit declaration of function 'strcat'

test/x86/emulator.c: In function 'test_cmps':
test/x86/emulator.c:26: warning: unused variable 'i'
test/x86/emulator.c: In function 'test_push':
test/x86/emulator.c:115: warning: 'tmp' is used uninitialized in this function

test/x86/lib/printf.c: In function 'vsnprintf':
test/x86/lib/printf.c:95: warning: unused variable 'n'

Signed-off-by: Bernhard Kaindl <bk@suse.de>
Signed-off-by: Avi Kivity <avi@qumranet.com>