tiny_ssim is built for the build host, not for the target platform.
Therefore, it mustn't include the config.h header, which is set up
specifically for the target platform and compiler.
This fixes cross building for older WinStore platforms, where
config.h contains "#define getenv(x) NULL".
Signed-off-by: Martin Storsjö <martin@martin.st>
tiny_ssim is build on the host, not the target and the HAVE_* are set for the
target.
This patch fixes building tiny_ssim when HAVE_* differed between target and host
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>