Makefile.package.in: optimize UPPERCASE macro

As noticed by Thomas, we call the UPPERCASE macro a lot, and it slows down
startup quite a bit.

Optimize it by implementing it in make, rather than forking a shell + tr.
The implementation is heavily based on the 'up' macro from gmsl
(http://gmsl.sf.net

)

With this in place, startup time is ~5 times lower.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>