When building the rts with ghc (e.g. using ghc as a c compiler), ghc's
"Value Add" is, it includes adding -include /path/to/ghcversion.h. For
this it looksup the rts package in the package database, which--if
empty--fails. Thus to allow compiling C files with GHC, we add the
-ghc-version flag, which takes the path to the ghcversion.h file.
A -no-ghc-version flag was omitted, as at that point it becomes
questionable why one would use ghc to compile c if one doesn't
any of the added value.
 from compiler/main/DriverPipeline.hs
- add package include paths even if we're just compiling .c
- files; this is the Value Add(TM) that using ghc instead of
- gcc gives you :)