Fix #12509: ghci -XSafe fails in an inscrutable way
Disable -XSafe temporarily while running internal GHCi expressions.
The issue is fixed in a similar way as tickets #13385 (closed) and #14342 (closed):
During GHCi startup we temporarily change the SafeHaskell flag
to Sf_None
to compile and execute GHCi internal expressions.
See merge request !23 for previous versions and related dicsussions of this patch.