[csmith-project/creduce] 22c349: Update info about dependencis of pre-build binary ...

[Eric Eide <noreply@github.com>]

  Branch: refs/heads/master
  Home:   https://github.com/csmith-project/creduce
  Commit: 22c349372ca59f6f88cc5a8d40b39ea4a190d118
      https://github.com/csmith-project/creduce/commit/22c349372ca59f6f88cc5a8d40b39ea4a190d118
  Author: Eric Eide <eeide@cs.utah.edu>
  Date:   2019-04-26 (Fri, 26 Apr 2019)

  Changed paths:
    M INSTALL.md

  Log Message:
  -----------
  Update info about dependencis of pre-build binary packages.

Pick a more recent OS as the example.  Update the wording to match the
current LLVM downloads website.  Mention that the Ubuntu 18.04 pre-built
binaries package also depends on `libxml2`.

(Actually, when using the Ubuntu 18.04 pre-built binaries package, the
current CMake-based build path *does not* require `libxml2`, because we
don't link against the components of LLVM that depend on that library.
The Autoconf-based build path is less precise in this regard.  It uses
`llvm-config --system-libs` to get the system libraries, and that answer
contains "-lxml2".  Whatever.  In the INSTALL instructions, just tell
people what kind of issues they might encounter.)