make the prl lookup search in standard locations

qtAddModule() skips adding standard library paths to LIBS. however, as
processPrlFiles() didn't know anything about that, it would not find the
prl files of qt libraries in these paths.
so centralize the definition of these default paths (we should actually
ask the linker for them) and use it in both places.
do the same for the include paths for symmetry.

Change-Id: I7e3692dc2d1c2d0c97a9151d15887b1263de137a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

mkspecs/common/unix.conf

@@ -13,4 +13,7 @@ QMAKE_PREFIX_SHLIB      = lib
 QMAKE_PREFIX_STATICLIB  = lib
 QMAKE_EXTENSION_STATICLIB = a
 
+QMAKE_DEFAULT_INCDIRS   = /usr/include /usr/local/include
+QMAKE_DEFAULT_LIBDIRS   = /usr/lib /usr/local/lib
+
 include(shell-unix.conf)

mkspecs/features/qt_functions.prf

@@ -45,10 +45,8 @@ defineTest(qtAddModule) {
     CONFIG += $$eval(QT.$${1}.CONFIG)
     DEFINES += $$eval(QT.$${1}.DEFINES)
 
-    unix {
-        MODULE_INCLUDES -= /usr/include /usr/local/include
-        MODULE_LIBS -= /usr/lib /usr/local/lib
-    }
+    MODULE_INCLUDES -= $$QMAKE_DEFAULT_INCDIRS
+    MODULE_LIBS -= $$QMAKE_DEFAULT_LIBDIRS
 
     INCLUDEPATH *= $$MODULE_INCLUDES
     auto_use_privates|isEqual(2, UsePrivate) { # Tests function parameter 2 ($$2) being equal to 'UsePrivate'

qmake/generators/unix/unixmake.cpp

@@ -578,6 +578,8 @@ void
 UnixMakefileGenerator::processPrlFiles()
 {
     QList<QMakeLocalFileName> libdirs, frameworkdirs;
+    foreach (const QString &dlib, project->values("QMAKE_DEFAULT_LIBDIRS"))
+        libdirs.append(QMakeLocalFileName(dlib));
     frameworkdirs.append(QMakeLocalFileName("/System/Library/Frameworks"));
     const QString lflags[] = { "QMAKE_LIBDIR_FLAGS", "QMAKE_FRAMEWORKPATH_FLAGS", "QMAKE_LFLAGS", "QMAKE_LIBS", QString() };
     for(int i = 0; !lflags[i].isNull(); i++) {