Fix compilation with latest MinGW-w64 (release 3)

Now that MinGW-w64 fixed the headers the old hack actually break stuff.

Change-Id: I1f60b9176982f6c07e01f3960bc1d7e70d7f9481
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
don't load wayland-scanner for all projects on linux

it's wasteful, given that exactly one add-on module (and most probably
nobody else) needs it.

i'd do the same with yacc and lex, but i suspect this would cause quite
an uproar.

Change-Id: Ic2a6ca19e829393835f824e31cd0893e78c3fd39
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Detect pointer size at configure-time on Windows-hosted builds

The configure-time procedure used on Windows does not currently
perform the same tests to determine the width of a pointer as are
performed on Unix-based builds.

This causes QT_POINTER_SIZE to be undefined in the generated
qconfig.h file. This in turn breaks compilation of various Qt modules
such as QtDeclarative.

This patch adds the same level of support for automatically
determining the target platform's pointer size, as is currently
offered to Unix users.

Change-Id: I93838c1759b14089ba9f4daf442048fb5c8da738
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>