QT configure script should respect $PKG_CONFIG

When cross-compiling QT, simply using `pkg-config` is bad as that will give you information about the host packages, not the target ones. simple fix is to behave like the upstream pkg-config m4 code: respect $PKG_CONFIG env var.

This simple change should fix the issue:
— a/configure
+++ b/configure
@@ -1772,7 +1772,7 @@ unixtests="$relpath/config.tests/unix"
mactests="$relpath/config.tests/mac"
WHICH="$unixtests/which.test"

-PKG_CONFIG=`$WHICH pkg-config 2>/dev/null`
+: ${PKG_CONFIG=`$WHICH pkg-config 2>/dev/null`}

1. find out which awk we want to use, prefer gawk, then nawk, then regular awk
   AWK=