Add pluginsdir to pkgconfig file

(cherry picked from commit 3a89e057b7)

qmake/generators/unix/unixmake2.cpp

@@ -1543,11 +1543,16 @@ UnixMakefileGenerator::writePkgConfigFile()     // ### does make sense only for
     QString includeDir = project->first("QMAKE_PKGCONFIG_INCDIR");
     if(includeDir.isEmpty())
 	includeDir = prefix + "/include";
+    QString pluginsDir = project->first("QMAKE_PKGCONFIG_PLUGINS");
+    if(pluginsDir.isEmpty())
+	pluginsDir = prefix + "/plugins";
 
     t << "prefix=" << prefix << endl;
     t << "exec_prefix=${prefix}\n"
       << "libdir=" << pkgConfigFixPath(libDir) << "\n"
       << "includedir=" << pkgConfigFixPath(includeDir) << endl;
+    // non-standard entry. Provides path for plugins
+    t << "pluginsdir=" << pkgConfigFixPath(pluginsDir) << endl;
     // non-standard entry. Provides useful info normally only
     // contained in the internal .qmake.cache file
     t << varGlue("CONFIG", "qt_config=", " ", "") << endl << endl;

src/qt.pro

@@ -177,6 +177,7 @@ unix {
    CONFIG     += create_libtool create_pc
    QMAKE_PKGCONFIG_LIBDIR = $$target.path
    QMAKE_PKGCONFIG_INCDIR = $$headers.path
+   QMAKE_PKGCONFIG_PLUGINS = $$plugins.path
 }
 
 wince-* {