make zlib_dependency auto-add QtCore as a private dep

our zlib header includes qglobal.h, so we need the qtcore include dirs,
and qtcore is also where the actual code is compiled into.

Change-Id: I09f530a1b4e6160438215a6d7223c0771ce94f05
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

mkspecs/features/qt_helper_lib.prf

@@ -13,6 +13,7 @@ load(qt_build_paths)
 
 TEMPLATE = lib
 CONFIG -= qt
+QT =  # In case qt is re-added.
 
 CONFIG -= warning_clean  # Don't presume 3rd party code to be clean
 load(qt_common)

src/3rdparty/zlib_dependency.pri

@@ -7,4 +7,8 @@ contains(QT_CONFIG, system-zlib) {
     }
 } else {
     INCLUDEPATH +=  $$PWD/zlib
+    !no_core_dep {
+        CONFIG += qt
+        QT_PRIVATE += core
+    }
 }

src/corelib/tools/tools.pri

@@ -158,6 +158,7 @@ else:SOURCES += tools/qelapsedtimer_generic.cpp
 contains(QT_CONFIG, zlib) {
     include($$PWD/../../3rdparty/zlib.pri)
 } else {
+    CONFIG += no_core_dep
     include($$PWD/../../3rdparty/zlib_dependency.pri)
 }
 

src/tools/bootstrap/bootstrap.pro

@@ -132,8 +132,12 @@ macx {
         ../../corelib/io/qstandardpaths_win.cpp
 }
 
-if(contains(QT_CONFIG, zlib)|cross_compile):include(../../3rdparty/zlib.pri)
-else:include(../../3rdparty/zlib_dependency.pri)
+contains(QT_CONFIG, zlib)|cross_compile {
+    include(../../3rdparty/zlib.pri)
+} else {
+    CONFIG += no_core_dep
+    include(../../3rdparty/zlib_dependency.pri)
+}
 
 win32:LIBS += -luser32 -lole32 -ladvapi32 -lshell32