contrib: qt: Backport two patches, fixing the mingw pkg-config files

Previously, the pkg-config files contained a broken "-D_UNICODE>", which caused build warnings on all Qt source files in VLC, like this:

In file included from <built-in>:464:
<command line>:16:17: warning: ISO C99 requires whitespace after the macro name [-Wc99-extensions]
   16 | #define _UNICODE> 1
      |                 ^

Backport a fix from upstream, getting rid of this. Also backport another patch to add a missing include statement.