GCC 4.8 brace initializer requires double braces

================================================

GCC 7 and clang work fine without the extra set of braces.

std::array<T, N> is an aggregate that contains a C array. To initialize it, you need outer braces for the class itself and inner braces for the C array:

https://stackoverflow.com/questions/12844475/why-cant-simple-initialize-with-braces-2d-stdarray

src/Mod/Sketcher/App/ExternalGeometryExtension.h

@@ -43,7 +43,7 @@ public:
     };
     // END_CREDIT_BLOCK: Credit under LGPL for this block to Zheng, Lei (realthunder) <realthunder.dev@gmail.com>
 
-    constexpr static std::array<const char *,NumFlags> flag2str { "Defining", "Frozen", "Detached","Missing", "Sync" };
+    constexpr static std::array<const char *,NumFlags> flag2str {{ "Defining", "Frozen", "Detached","Missing", "Sync" }};
 
     ExternalGeometryExtension() = default;
     virtual ~ExternalGeometryExtension() = default;