Simplify header-only mode usage

It's sufficient to define PUGIXML_HEADER_ONLY anywhere now, source is included
automatically.

This is a second attempt; this time it includes a workaround for QMake bug
that caused it to generate incorrect Makefile.

src/pugiconfig.hpp

@@ -39,7 +39,6 @@
 
 // Uncomment this to switch to header-only version
 // #define PUGIXML_HEADER_ONLY
-// #include "pugixml.cpp"
 
 // Uncomment this to enable long long support
 // #define PUGIXML_HAS_LONG_LONG

src/pugixml.hpp

@@ -1329,6 +1329,13 @@ namespace std
 
 #endif
 
+// Make sure implementation is included in header-only mode
+// Use macro expansion in #include to work around QMake (QTBUG-11923)
+#if defined(PUGIXML_HEADER_ONLY) && !defined(PUGIXML_SOURCE)
+#	define PUGIXML_SOURCE "pugixml.cpp"
+#	include PUGIXML_SOURCE
+#endif
+
 /**
  * Copyright (c) 2006-2014 Arseny Kapoulkine
  *

tests/test_header_only.cpp

@@ -0,0 +1,16 @@
+#define PUGIXML_HEADER_ONLY
+#define pugi pugih
+
+#include "common.hpp"
+
+// Check header guards
+#include "../src/pugixml.hpp"
+#include "../src/pugixml.hpp"
+
+TEST(header_only)
+{
+	xml_document doc;
+	CHECK(doc.load_string(STR("<node/>")));
+	CHECK_STRING(doc.first_child().name(), STR("node"));
+	CHECK(doc.first_child() == doc.select_node(STR("//*")).node());
+}