message: build: add linker optimization flags to gitian descriptors
  Any -O argument will enable optimizations in GNU ld. We can use -O2
  here, as this matches our compile flags. Note that this would also
  enable additional optimizations if using the lld or gold linkers,
  when compared to -O0.
diff: @@ -46,7 +46,7 @@ script: |
  FAKETIME_PROGS="date ar ranlib nm"
  HOST_CFLAGS="-O2 -g"
  HOST_CXXFLAGS="-O2 -g"
  - HOST_LDFLAGS_BASE="-static-libstdc++"
  + HOST_LDFLAGS_BASE="-static-libstdc++ -Wl,-O2"
  export QT_RCC_TEST=1
  export QT_RCC_SOURCE_DATE_OVERRIDE=1
  