This bug can be reproduced by doing
guix package -i ghc
echo 'main=return()' > test.hs
ghc test.hs
The expected output is that the program will be compiled, but instead we
get the error message
gcc: error trying to exec 'as': execvp: No such file or directory
`gcc' failed in phase `C Compiler'. (Exit code: 1)
The error is caused, of course, by as not being found in the path.
Interestingly, though, the error occurs in gcc, which fails to find as.
The general path for compiling things with gcc is to use gcc-toolchain,
which brings as and others into the profile, but as ghc calls gcc
directly (with no gcc-toolchain), ghc fails to actually compile anything.
