Changed more variables with the convention to use .ext rather than _EXT.
For example, replace PREFIX_DLL with PREFIX.dll.
Signed-off-by: Christophe de Dinechin <christophe@dinechin.org>
This addresses two issues:
- There was a mixup between the installed config.system-setup.mk
and the one being used for installation, which could lead to
build fragility / difficulty to reproduce.
- Making `make install` and `rpmbuild` consistent in what is
being installed and produced.