[ELF] Implemented -Bsymbolic-functions command line option

-Bsymbolic-functions: 
When creating a shared library, bind references to global 
function symbols to the definition within the shared library, if any.

This patch also fixed behavior of already existent -Bsymbolic:
previously PLT entries were created even if -Bsymbolic was specified.

Differential revision: http://reviews.llvm.org/D16411

llvm-svn: 259481
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 4fbf202..677d40b 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -188,6 +188,7 @@
 
   Config->AllowMultipleDefinition = Args.hasArg(OPT_allow_multiple_definition);
   Config->Bsymbolic = Args.hasArg(OPT_Bsymbolic);
+  Config->BsymbolicFunctions = Args.hasArg(OPT_Bsymbolic_functions);
   Config->Demangle = !Args.hasArg(OPT_no_demangle);
   Config->DiscardAll = Args.hasArg(OPT_discard_all);
   Config->DiscardLocals = Args.hasArg(OPT_discard_locals);