This allows building two versions for different architectures at
the same time, without the built files clobbering each other.
This is very helpful when trying to track down differences between
two build configurations.
To build outside of the source tree, create the other directory to
use for building (either outside of the openh264 directory, or as
a subdirectory), enter that directory, and do
"make -f path/to/openh264/Makefile".
This reverts commit 09025dc8ef3e20403ad2a925287e6b418851f778.
There is no need to set ASM_ARCH unless assembly sources actually
are built. ASM_ARCH is no longer used for setting unrelated CFLAGS.
