vsnprintf: Change print_itoa to use less stack

Remove recursive call in print_itoa to reduce the stack usage.

Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Include stdint.h for libc/test/run-time.c, fixing build

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Merge branch 'update-2.1.1.1'