build: remove architecture flag as default C flag

build: remove architecture flag as default C flag

Any flags added to the project args are automatically added to all builds,
both native and cross-compiled. This is not what we want for the -march
flag as a valid -march for the cross-compile is not valid for pmdinfogen
which is a native-build tool.

Instead we store the march flag as a variable, and add it to the default
cflags for all libs, drivers, examples, etc. This will allow pmdinfogen to
compile successfully in a cross-compilation environment.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Luca Boccassi <bluca@debian.org>