People do not read (the Warning about --lib is regularly ignored)

[TomMD]

Describe the bug

People show up at various places around the internet with complaints about cabal install not installing their library (see this recent example: https://stackoverflow.com/questions/62073719/why-is-installing-a-haskell-package-not-working).

To Reproduce

1. Make a useful tool
2. Gain popularity
3. Change it's behavior
4. Let humans be humans

Expected behavior
People read.

Additional context

I think we need the line:

Warning: You asked to install executables, but there are no executables in
target: binary-bits. Perhaps you want to use --lib to install libraries
instead

To be bold and red when the terminal allows. Thoughts?

I'm not sure how to do this portably, but direct use of escape sequences does work:

Prelude> putStrLn "\x1b[31m Warning: You asked to install executables \x1b[0m"
 Warning: You asked to install executables
--- ^^^ That's red

[TomMD]

See #6857 for the fix.