streamline libdl detection and linking

instead of having a library and a test, use a library with two sources,
the first being empty (i.e., just libc). this allows us doing away with
the "libdl" feature, and using just the "dlopen" one.

subsequently, replace all LIBS+=$$QMAKE_LIBS_DYNLOAD with
QMAKE_USE+=libdl.
the definitions of QMAKE_LIBS_DYNLOAD remain in the qmakespecs for
backwards compat only. n.b.: the only specs where it is not empty or
"-ldl" (i.e., what we support now) are the hpux ones, where the library
is called 'dld'.

technically, the "library" feature should depend on '!unix || dlopen', but
that's for a later patch.

Change-Id: Ib8546affc4b7bc757f1a76729573ddd00e152176
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/corelib/configure.json

@@ -74,10 +74,10 @@
             ]
         },
         "libdl": {
-            "label": "dlopen() in libdl",
-            "export": "",
+            "label": "dlopen()",
             "test": "unix/dlopen",
             "sources": [
+                "",
                 "-ldl"
             ]
         },
@@ -131,11 +131,6 @@
             "type": "compile",
             "test": "unix/cloexec"
         },
-        "dlopen": {
-            "label": "dlopen() in libc",
-            "type": "compile",
-            "test": "unix/dlopen"
-        },
         "eventfd": {
             "label": "eventfd",
             "type": "compile",
@@ -211,12 +206,8 @@
         },
         "dlopen": {
             "label": "dlopen()",
-            "condition": "tests.dlopen || libs.libdl"
-        },
-        "libdl": {
-            "label": "dlopen() in libdl",
-            "condition": "!tests.dlopen && libs.libdl",
-            "output": [ { "type": "privateConfig", "negative": true } ]
+            "condition": "config.unix && libs.libdl",
+            "output": [ "privateFeature" ]
         },
         "doubleconversion": {
             "label": "DoubleConversion",

src/corelib/plugin/plugin.pri

@@ -35,4 +35,4 @@ integrity {
 	SOURCES += plugin/qlibrary_unix.cpp
 }
 
-!no-libdl: LIBS_PRIVATE += $$QMAKE_LIBS_DYNLOAD
+qtConfig(dlopen): QMAKE_USE_PRIVATE += libdl

src/platformsupport/eglconvenience/eglconvenience.pro

@@ -38,6 +38,6 @@ qtConfig(xlib) {
 }
 CONFIG += egl
 
-LIBS_PRIVATE += $$QMAKE_LIBS_DYNLOAD
+qtConfig(dlopen): QMAKE_USE += libdl
 
 load(qt_module)

src/plugins/platforms/eglfs/eglfsdeviceintegration.pro

@@ -17,8 +17,6 @@ QT += \
 qtHaveModule(input_support-private): \
     QT += input_support-private
 
-LIBS += $$QMAKE_LIBS_DYNLOAD
-
 # Avoid X11 header collision, use generic EGL native types
 DEFINES += QT_EGL_NO_X11
 

src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp

@@ -54,7 +54,7 @@
 #include <QtGlxSupport/private/qglxconvenience_p.h>
 #include <QtPlatformHeaders/QGLXNativeContext>
 
-#if defined(Q_OS_LINUX) || defined(Q_OS_BSD4)
+#if !defined(QT_STATIC) && QT_CONFIG(dlopen)
 #include <dlfcn.h>
 #endif
 
@@ -564,7 +564,7 @@ QFunctionPointer QGLXContext::getProcAddress(const char *procName)
     if (!glXGetProcAddressARB) {
         QList<QByteArray> glxExt = QByteArray(glXGetClientString(m_display, GLX_EXTENSIONS)).split(' ');
         if (glxExt.contains("GLX_ARB_get_proc_address")) {
-#if defined(Q_OS_LINUX) || defined(Q_OS_BSD4)
+#if QT_CONFIG(dlopen)
             void *handle = dlopen(NULL, RTLD_LAZY);
             if (handle) {
                 glXGetProcAddressARB = (qt_glXGetProcAddressARB) dlsym(handle, "glXGetProcAddressARB");

src/plugins/platforms/xcb/gl_integrations/xcb_glx/xcb_glx.pro

@@ -12,7 +12,7 @@ qtConfig(xcb-glx) {
     QMAKE_USE += xcb_glx
 }
 
-LIBS += $$QMAKE_LIBS_DYNLOAD
+!static:qtConfig(dlopen): QMAKE_USE += libdl
 
 HEADERS += \
     qxcbglxintegration.h \