-betterC working on GDC

-added some attributes like export and nothrow

dub.json

@@ -56,9 +56,18 @@
 			"name" : "dynlib-betterC",
 			"targetType" : "dynamicLibrary",
 			"dflags": [
-				"-betterC",
-				"-defaultlib=",
-				"--fvisibility=hidden"
+				"-betterC"
+			],
+			"dflags-ldc": [
+				"--fvisibility=hidden",
+				"-link-defaultlib-shared"
+			],
+			"dflags-gdc": [
+				"-fno-druntime",
+				"-fvisibility=hidden"
+			],
+			"lflags-gdc": [
+				"-lpthread"
 			]
 		},
 		{
@@ -69,8 +78,13 @@
 				"source\/win_dll.d"
 			],
 			"dflags": [
-				"-betterC",
-				"-defaultlib="
+				"-betterC"
+			],
+			"dflags-gdc": [
+				"-fno-druntime"
+			],
+			"lflags-gdc": [
+				"-lpthread"
 			]
 		}
 	]