This is an important usability problem with the current build scripts.  In
particular:

1. When configuring, autoconf should check whether the CFE is found (in the
   specified directory) and works.  If not, print out LOUD warnings, but do
   not set LLVMGCCPATH in the Makefile.config.

2. When building the runtime directory, don't build subdirs if the LLVMGCCPATH
   variable is not set, instead, print out another loud warning.

This is really important because this seems to be, by far, the most serious
end-user problem encountered by people.  Especially since the getting started
guide was broken in the 1.0 release.

-Chris

When fixing this, we must keep in mind the need to be able to bootstrap the
C/C++FE sanely; someone should update the CFEBuildInstrs.html document. (I can
if no one else wants to, but it will be trial and error for me....)

Item 2, above, is done. (Someone should double-check my work on that Makefile to
make sure it looks OK.)  In Chris's original comment, I think he meant LLVMGCCDIR.

Whoops, I meant to assign this to myself....

Ok, item 1 is done too. I've done some testing locally, but please feel free to
check it out.

http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20031110/009551.html
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20031110/009553.html

The makefile changes look wonderful.  John, please take a look at the configure
changes to make sure you're happy with them.

Thanks Brian!!

-Chris