Attempt to fix build failure with GCC 5.4.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@352435 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/ELF/ScriptParser.cpp b/ELF/ScriptParser.cpp
index 324c00e..03a66f8 100644
--- a/ELF/ScriptParser.cpp
+++ b/ELF/ScriptParser.cpp
@@ -384,8 +384,8 @@
     skip();
 }
 
-static std::tuple<ELFKind, uint16_t> parseBfdName(StringRef S) {
-  return StringSwitch<std::tuple<ELFKind, uint16_t>>(S)
+static std::pair<ELFKind, uint16_t> parseBfdName(StringRef S) {
+  return StringSwitch<std::pair<ELFKind, uint16_t>>(S)
       .Case("elf32-i386", {ELF32LEKind, EM_386})
       .Case("elf32-iamcu", {ELF32LEKind, EM_IAMCU})
       .Case("elf32-littlearm", {ELF32LEKind, EM_ARM})