Install script with cabal: check there is one ghc in $PATH

[jneira]

• It throws an error if there is no one

D:\ws\haskell\haskell-ide-engine>cabal v2-run .\install.hs -w D:\bin\ghc-8.6.5\bin\ghc  --project-file=install\shake.project
........
********************************************************************************

No ghc installations found in $PATH.
The script requires at least one ghc in $PATH to be able to build hie.

********************************************************************************


No ghc installations found in $PATH.
The script requires at least one ghc in $PATH to be able to build hie.

CallStack (from HasCallStack):
  error, called at src\Env.hs:79:3 in hie-install-0.8.0.0-inplace:Env

Closes #1620

[fendor]

LGTM! thank you!