Corrected the Table of Contents.

Corrected the Table of Contents.
Corrected capitalization of subheadings.
Created a new subsection for compiling the C front end and moved all references
to it there.
Updated the disk space requirements to reflect the need for the binary C front
end and the optional C front end source.
Added information on unpacking the distribution to the summary section.
Moved autoconf environment variables to the autoconf section.
Changed make to gmake.
Removed some of the precise directions for unpacking the archives.
Fixed some formatting inconsistencies (headings that were not centered).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7132 91177308-0d34-0410-b5e6-96231b3b80d8