Gitian fixes for 0.9.0rc1 build

- Add 'g++' package (virtualbox images don't have this by default)
- Workaround for determinism in Qt5 resources
- Pass --disable-maintainer-mode --disable-dependency-tracking to
  configure for libqrencode to avoid random errors about missing m4
  directory
- Fix typo -with-pic -> --with-pic

It is not necessary to rebuild dependencies after this commit.
Fixes #3610 and #3612.

contrib/gitian-descriptors/gitian-linux.yml

@@ -6,6 +6,7 @@ architectures:
 - "i386"
 - "amd64"
 packages: 
+- "g++"
 - "libqt4-dev"
 - "git-core"
 - "unzip"