I get a number of warnings (see below). The warnings about the large decimal constants seem worrying: is it supposed to be like this?
Yes, these warnings are normal. They occur in C code generated for the maximum and minimum bounds of the Int/Int32/Int64 types. The minimum Int value of -2147483648, when expressed literally in C, generates a warning from gcc that the decimal constant is so large it is unsigned. If you think this message is misleading, I agree, and I suggest you should report it as a bug to Gnu.
The build failed, because I have no Java (which, I think, was not mentioned in the installation documents). To what extent will this limit my options?
The only requirement for Java is to build the hat-trail browser and the HOOD browser. (This is mentioned near the top of the installation page, under System Requirements.) Do not worry if you don't wish to use these particular debugging tools - the rest of the nhc98 build is complete. (For the future, we are working to remove Java as a requirement for the hat-trail browser, by redesigning and recoding it in Haskell.) Regards, Malcolm