GHCI error message is unclear when passing option-like settings to GHCI

[mgsloan]

From https://stackoverflow.com/questions/45640896/how-to-pass-stack-ghci-rts-options

$ stack ghci -- Main.hs +RTS -M20M
Cannot use 'stack ghci' with both file targets and build targets

Issue is that it is doing the check for having both file and package targets without parsing the build targets. Instead, would be good to fail with a target parse error + a suggestion to use --ghci-options

[mgsloan]

Fixed!