configure: Drop unused AC_PROG_CPP
In configure, we were calling AC_PROG_CPP
but never making use of the
$CPP variable it sets or reads.
The issue is $CPP will show up in the --help output of configure, falsely advertising a configuration option that does nothing.
What we ultimately want to configure is the haskell preprocessor, which could potentially be done through the $CPP env variable but isn't (see m4/fp_cpp_cmd_with_args.m4
).
The reason we don't use the $CPP variable is because HS_CPP_CMD is
expected to be a single command (without flags), but AC_PROG_CPP, when
CPP is unset, will set said variable to something like /usr/bin/gcc -E
.
Instead, we configure HS_CPP_CMD through $CC
I couldn't find occurrences of the variable $CPP ever being used...