message: Litecoin: Make it easier to specify gbuild resource limits
  Add variables for gbuild thread and memory limits.  Simplifies using custom values.
diff: @@ -113,17 +113,20 @@ The gbuild invocations below <b>DO NOT DO THIS</b> by default.
  ### Build and sign Litecoin Core for Linux, Windows, and macOS:
  + export GITIAN_THREADS=2
  + export GITIAN_MEMORY=3000
  +
  pushd ./gitian-builder
  - ./bin/gbuild --num-make 2 --memory 3000 --commit litecoin=v${VERSION} ../litecoin/contrib/gitian-descriptors/gitian-linux.yml
  + ./bin/gbuild --num-make $GITIAN_THREADS --memory $GITIAN_MEMORY --commit litecoin=v${VERSION} ../litecoin/contrib/gitian-descriptors/gitian-linux.yml
  ./bin/gsign --signer "$SIGNER" --release ${VERSION}-linux --destination ../gitian.sigs.ltc/ ../litecoin/contrib/gitian-descriptors/gitian-linux.yml
  mv build/out/litecoin-*.tar.gz build/out/src/litecoin-*.tar.gz ../
  - ./bin/gbuild --num-make 2 --memory 3000 --commit litecoin=v${VERSION} ../litecoin/contrib/gitian-descriptors/gitian-win.yml
  + ./bin/gbuild --num-make $GITIAN_THREADS --memory $GITIAN_MEMORY --commit litecoin=v${VERSION} ../litecoin/contrib/gitian-descriptors/gitian-win.yml
  ./bin/gsign --signer "$SIGNER" --release ${VERSION}-win-unsigned --destination ../gitian.sigs.ltc/ ../litecoin/contrib/gitian-descriptors/gitian-win.yml
  mv build/out/litecoin-*-win-unsigned.tar.gz inputs/litecoin-win-unsigned.tar.gz
  mv build/out/litecoin-*.zip build/out/litecoin-*.exe ../
  - ./bin/gbuild --num-make 2 --memory 3000 --commit litecoin=v${VERSION} ../litecoin/contrib/gitian-descriptors/gitian-osx.yml
  + ./bin/gbuild --num-make $GITIAN_THREADS --memory $GITIAN_MEMORY --commit litecoin=v${VERSION} ../litecoin/contrib/gitian-descriptors/gitian-osx.yml
  ./bin/gsign --signer "$SIGNER" --release ${VERSION}-osx-unsigned --destination ../gitian.sigs.ltc/ ../litecoin/contrib/gitian-descriptors/gitian-osx.yml
  mv build/out/litecoin-*-osx-unsigned.tar.gz inputs/litecoin-osx-unsigned.tar.gz
  mv build/out/litecoin-*.tar.gz build/out/litecoin-*.dmg ../
  