build: run configure script from builddir rather than srcdir

Based on an equivalent patch from Philip Withnall <philip@tecnocode.co.uk>
for libmbim; see:

    https://bugs.freedesktop.org/show_bug.cgi?id=94639

autogen.sh

@@ -17,8 +17,8 @@ PKG_NAME=ModemManager
     gtkdocize || exit 1
     autopoint --force
     AUTOPOINT='intltoolize --automake --copy' autoreconf --force --install --verbose
-    if test -z "$NOCONFIGURE"; then
-        ./configure --enable-maintainer-mode "$@"
-    fi
 )
 
+if test -z "$NOCONFIGURE"; then
+    $srcdir/configure --enable-maintainer-mode "$@"
+fi