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/deps-linux.yml

@@ -6,6 +6,7 @@ architectures:
 - "i386"
 - "amd64"
 packages:
+- "g++"
 - "unzip"
 - "zip"
 - "pkg-config"
@@ -50,7 +51,7 @@ script: |
   tar xjfm qrencode-3.4.3.tar.bz2
   cd qrencode-3.4.3
   #   need --with-pic to avoid relocation error in 64 bit builds
-  ./configure --prefix=$STAGING --enable-static --disable-shared -with-pic --without-tools
+  ./configure --prefix=$STAGING --enable-static --disable-shared --with-pic --without-tools --disable-maintainer-mode --disable-dependency-tracking
   make $MAKEOPTS install
   cd ..
   #