Merge pull request #5771 from jsquyres/pr/v4.0.x/readme-update-configure-cli-with-options

v4.0.x: README: Add note about --with-foo and RPATH

README

@@ -8,7 +8,7 @@ Copyright (c) 2004-2008 High Performance Computing Center Stuttgart,
                         University of Stuttgart.  All rights reserved.
 Copyright (c) 2004-2007 The Regents of the University of California.
                         All rights reserved.
-Copyright (c) 2006-2017 Cisco Systems, Inc.  All rights reserved.
+Copyright (c) 2006-2018 Cisco Systems, Inc.  All rights reserved.
 Copyright (c) 2006-2011 Mellanox Technologies. All rights reserved.
 Copyright (c) 2006-2012 Oracle and/or its affiliates.  All rights reserved.
 Copyright (c) 2007      Myricom, Inc.  All rights reserved.
@@ -765,6 +765,26 @@ Open MPI is unable to find relevant support for <foo>, configure will
 assume that it was unable to provide a feature that was specifically
 requested and will abort so that a human can resolve out the issue.
 
+Additionally, if a search directory is specified in the form
+--with-<foo>=<dir>, Open MPI will:
+
+1. Search for <foo>'s header files in <dir>/include.
+2. Search for <foo>'s library files:
+   2a. If --with-<foo>-libdir=<libdir> was specified, search in
+       <libdir>.
+   2b. Otherwise, search in <dir>/lib, and if they are not found
+       there, search again in <dir>/lib64.
+3. If both the relevant header files and libraries are found:
+   3a. Open MPI will build support for <foo>.
+   3b. If the root path where the <foo> libraries are found is neither
+       "/usr" nor "/usr/local", Open MPI will compile itself with
+       RPATH flags pointing to the directory where <foo>'s libraries
+       are located.  Open MPI does not RPATH /usr/lib[64] and
+       /usr/local/lib[64] because many systems already search these
+       directories for run-time libraries by default; adding RPATH for
+       them could have unintended consequences for the search path
+       ordering.
+
 INSTALLATION OPTIONS
 
 --prefix=<directory>