hadrian: Add multi:<pkg> and multi targets for starting a multi-repl

This patch adds support to hadrian for starting a multi-repl containing
all the packages which stage0 can build. In particular, there is the new
user-facing command:

```
./hadrian/ghci-multi
```

which when executed will start a multi-repl containing the `ghc` package
and all it's dependencies.

This is implemented by two new hadrian targets:

```
./hadrian/build multi:<pkg>
```

Construct the arguments for a multi-repl session where the top-level
package is <pkg>. For example, `./hadrian/ghci-multi` is implemented
using `multi:ghc` target.

There is also the `multi` command which constructs a repl for everything
in stage0 which we can build.

1 files changed, 1 insertions, 1 deletions

diff --git a/configure.ac b/configure.ac
index e6c9ed6ec7..71b5f680cf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1179,7 +1179,7 @@ fi
 # Create the configuration for the Hadrian build system if it is present
 if test -e hadrian/cfg/system.config.in; then
     AC_CONFIG_FILES([hadrian/cfg/system.config])
-    AC_CONFIG_FILES([hadrian/ghci-cabal hadrian/ghci-stack])
+    AC_CONFIG_FILES([hadrian/ghci-cabal hadrian/ghci-stack hadrian/ghci-multi-cabal])
 fi
 
 # We got caught by