[m-rev.] diff: update README.MacOS

[Julien Fischer]

Branches: main, 12.08

README.MacOS:
     Update for Mac OS 10.8.

Julien.

Index: README.MacOS
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/README.MacOS,v
retrieving revision 1.23
diff -u -r1.23 README.MacOS
--- README.MacOS	20 Dec 2011 06:40:02 -0000	1.23
+++ README.MacOS	5 Nov 2012 05:35:34 -0000
@@ -1,18 +1,19 @@
  This file documents the port of Mercury to Mac OS X,
  i.e. the "*-apple-darwin*" configuration.

-=========================================================
-IMPORTANT NOTE FOR FOR USERS OF MAC OS X 10.7 AND XCODE 4
-=========================================================
-
-The default C compiler provided in XCode 4 is llvm-gcc.
-Mercury does NOT work with llvm-gcc.  In order to build Mercury you will either
-need to use one of the other C compilers available on the system, either GCC
-4.2 or clang.  With XCode 4 "gcc" is actually a symbolic link for llvm-gcc; the
-GCC 4.2 executable is named "gcc-4.2".
-
-Alternatively, the MacPorts project, <http://www.macports.org/>, provides more
-recent versions of GCC for Mac OS X.
+================================================================
+IMPORTANT NOTE FOR FOR USERS OF MAC OS X 10.7 AND 10.8 (XCODE 4)
+================================================================
+
+The default C compiler provided with XCode 4.* is llvm-gcc.
+Mercury does NOT work with llvm-gcc.  Note that with XCode 4.* the executable
+named "gcc" is actually a symbolic link for llvm-gcc.
+
+In order to build Mercury you will need to a C compiler other than llvm-gcc,
+for example clang (See README.clang for further details) or actual GCC.  Recent
+version of XCode no longer ship actual GCC, so if you wish to use that you will
+need to install it yourself.  (The MacPorts project,
+<http://www.macports.org/>, provides more recent versions of GCC for Mac OS X.)

  As llvm-gcc is no longer supported as of version 3.0 of LLVM, we have no
  intention of ever supporting Mercury with it.