Hadrian: running the testsuite with cross-compilers

Hadrian fails to run the testsuite when GHC is built as a cross-compiler.

>./configure --target=aarch64-linux-gnu
> ./hadrian/build-stack --flavour=quick --bignum=native --docs=none test
| Run Testsuite GetExtraDeps: none
Unknown program "_build/stage1/lib/bin/aarch64-linux-gnu-ghc-iserv"
Build failed.

Expected

• Support running the testsuite as shown above !7850 (closed)
• Automatically switch off Haddock tests so that we don't have to pass --docs=none
• Skip tests requiring to run built test programs (they won't as we are cross-compiling)
• Add an option to run built test programs through a user-specified wrapper (qemu-*, nodejs...)
• Add an option to specify the iserv program to use and its options