cd /var/tmp

cat > a.c <<EOT
#include <tiffconf.h>
#include <stdio.h>

int main(void) {
        printf("8=%d\n", sizeof(TIFF_INT64_T));
        printf("8=%d\n", sizeof(TIFF_UINT64_T));
        printf("%d=%d\n", sizeof(ssize_t), sizeof(TIFF_SSIZE_T));
}
EOT

GCC=gcc
CC=/ws/on12-tools/SUNWspro/solarisstudio12.4/bin/cc

$GCC -m32 a.c && ./a.out
$GCC -m64 a.c && ./a.out
$CC -m32 a.c && ./a.out
$CC -m64 a.c && ./a.out

Output should be:
8=8
8=8
4=4
...
8=8
8=8
8=8
...
8=8
8=8
4=4
...
8=8
8=8
8=8