libflac patch breaks build on Linux

[Emmanuel Kasper]

Hello

I have seen today by building mame on a new computer, that our libflac
patch breaks building mame on Linux if people set BUILD_FLAC=1

the problem is that we changed the include path like this:

-#include "../../lib/libflac/include/flac/all.h"
+#include <FLAC/all.h>

this will work on OSX and Windows since they have case insensitive file
systems by default

but on Linux with BUILD_FLAC=1 it will fail because the compiler will
not find lib/libflac/include/FLAC/ in the mame-distributed flac (notice
the uppercase)

I missed this before because I did not rebuilt mame from scratch when
testing the switch, I only called the build target again

Maybe it is possible to ask the mame guys to rename the include dir to
lib/libflac/include/FLAC/ (as upstream libflac is), but as they mainly
work from Windows, I don't know if it is technically possible

Manu