ELF: Use hidden visibility for all DefinedSynthetic symbols.

This simplifies the code by allowing us to remove the visibility argument
to functions that create synthetic symbols.

The only functional change is that the visibility of the MIPS "_gp" symbol
is now hidden. Because this symbol is defined in every executable or DSO, it
would be difficult to observe a visibility change here.

Differential Revision: http://reviews.llvm.org/D19033

llvm-svn: 266208
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
index a0d0769..4e9b623 100644
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -296,9 +296,8 @@
 
 template <typename ELFT>
 DefinedSynthetic<ELFT>::DefinedSynthetic(StringRef N, uintX_t Value,
-                                         OutputSectionBase<ELFT> &Section,
-                                         uint8_t StOther)
-    : Defined(SymbolBody::DefinedSyntheticKind, N, STB_GLOBAL, StOther,
+                                         OutputSectionBase<ELFT> &Section)
+    : Defined(SymbolBody::DefinedSyntheticKind, N, STB_GLOBAL, STV_HIDDEN,
               0 /* Type */),
       Value(Value), Section(Section) {}