[Patch, Darwin + doc] alias mconstant-cfstrings to fconstant-cfstrings and document the flag.

[IainS]

The Apple system tools expect the "-mconstant-cfstrings" to be "- 
fconstant-cfstrings".

the patch below aliases this, for compatibility and provides an entry  
in invoke.texi

OK for trunk?
Iain


Index: gcc/config/darwin.opt
===================================================================
--- gcc/config/darwin.opt	(revision 170138)
+++ gcc/config/darwin.opt	(working copy)
@@ -64,6 +64,9 @@ Driver Alias(Zdynamiclib)
  exported_symbols_list
  Driver Separate Alias(Zexported_symbols_list)

+fconstant-cfstrings
+Driver Alias(mconstant-cfstrings)
+
  filelist
  Driver RejectNegative Separate

Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi	(revision 170138)
+++ gcc/doc/invoke.texi	(working copy)
@@ -510,7 +510,7 @@ Objective-C and Objective-C++ Dialects}.
  -dead_strip @gol
  -dependency-file  -dylib_file  -dylinker_install_name @gol
  -dynamic  -dynamiclib  -exported_symbols_list @gol
--filelist  -flat_namespace  -force_cpusubtype_ALL @gol
+-fconstant-cfstrings -filelist  -flat_namespace  - 
force_cpusubtype_ALL @gol
  -force_flat_namespace  -headerpad_max_install_names @gol
  -iframework @gol
  -image_base  -init  -install_name  -keep_private_externs @gol
@@ -10811,6 +10811,14 @@ for executables, @file{ld}, will quietly give  
the
  restrictive subtype of any of its input files.

  @table @gcctabopt
+@item -fconstant-cfstrings
+@opindex fconstant-cfstrings
+Enable the automatic creation of a CoreFoundation-type constant string
+whenever a special builtin @code{__builtin__CFStringMakeConstantString}
+is called on a literal string.  This will also override the
+@option{-fconstant-string-class} setting and cause @code{@@"@dots{}"}
+literals to be laid out as constant CoreFoundation strings.
+
  @item -F@var{dir}
  @opindex F
  Add the framework directory @var{dir} to the head of the list of