Revert back to previous building behaviour on *nix/Mac systems

This is based on the feedback from @p12tic, and I also think it might
lead to a regression on systems that don't have the correct version of CMake,
and/or a Make implementation that doesn't support "-C".

Signed-off-by: Dom Rodriguez <shymega@shymega.org.uk>

clean_build.sh

@@ -39,13 +39,13 @@ fi
 git submodule update --init --recursive
 
 rm -rf ./build
+mkdir build
+cd ./build
 
-# Previous versions of this script created the build directory, and CD'd into it - CMake allows us to do this another way...
-
-$B_CMAKE "$B_CMAKE_FLAGS" -B build || exit 1
+$B_CMAKE "$B_CMAKE_FLAGS" .. || exit 1
 
 echo "INFO: Now commencing Barrier build process..."
 echo "INFO: We're building an $B_BUILD_TYPE output type."
-$(command -v make) -C build || exit 1
+$(command -v make) || exit 1
 
 exit