Document -fno-merge-debug-strings rather than -fmerge-debug-strings.

From-SVN: r131631

gcc/doc/invoke.texi

@@ -304,7 +304,7 @@ Objective-C and Objective-C++ Dialects}.
 -ftest-coverage  -ftime-report -fvar-tracking @gol
 -g  -g@var{level}  -gcoff -gdwarf-2 @gol
 -ggdb  -gstabs  -gstabs+  -gvms  -gxcoff  -gxcoff+ @gol
--fmerge-debug-strings -fdebug-prefix-map=@var{old}=@var{new} @gol
+-fno-merge-debug-strings -fdebug-prefix-map=@var{old}=@var{new} @gol
 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
 -p  -pg  -print-file-name=@var{library}  -print-libgcc-file-name @gol
@@ -4162,8 +4162,9 @@ The default is @samp{-femit-struct-debug-detailed=all}.
 
 This option works only with DWARF 2.
 
-@item -fmerge-debug-strings
+@item -fno-merge-debug-strings
 @opindex fmerge-debug-strings
+@opindex fno-merge-debug-strings
 Direct the linker to merge together strings which are identical in
 different object files.  This is not supported by all assemblers or
 linker.  This decreases the size of the debug information in the