Fix typo in libtool --help output.

[Ralf Wildenhues]

I'll be pushing this trivial patch.

Thanks,
Ralf

    Fix typo in libtool --help output.
    
    * libltdl/config/ltmain.m4sh (func_mode_help): Fix typo in help
    output.

diff --git a/libltdl/config/ltmain.m4sh b/libltdl/config/ltmain.m4sh
index 9790579..cdc23a5 100644
--- a/libltdl/config/ltmain.m4sh
+++ b/libltdl/config/ltmain.m4sh
@@ -1055,8 +1055,8 @@ This mode accepts the following additional options:
 
   -o OUTPUT-FILE    set the output file name to OUTPUT-FILE
   -no-suppress      do not suppress compiler output for multiple passes
-  -prefer-pic       try to building PIC objects only
-  -prefer-non-pic   try to building non-PIC objects only
+  -prefer-pic       try to build PIC objects only
+  -prefer-non-pic   try to build non-PIC objects only
   -shared           do not build a \`.o' file suitable for static linking
   -static           only build a \`.o' file suitable for static linking
   -Wc,FLAG          pass FLAG directly to the compiler