Try harder to fix GCC 5.3 build

(This time verified locally.)

It was failing with:

llvm/lib/MC/XCOFFObjectWriter.cpp:168:56: error: array must be initialized with a brace-enclosed initializer
   std::array<Section *const, 2> Sections = {&Text, &BSS};
                                                        ^

Author: zmodem

llvm/lib/MC/XCOFFObjectWriter.cpp

@@ -165,7 +165,7 @@ class XCOFFObjectWriter : public MCObjectWriter {
 
   // All the XCOFF sections, in the order they will appear in the section header
   // table.
-  std::array<Section *const, 2> Sections = {&Text, &BSS};
+  std::array<Section *const, 2> Sections{{&Text, &BSS}};
 
   CsectGroup &getCsectGroup(const MCSectionXCOFF *MCSec);