Fix duplicates in QMAKE_DIR_REPLACE

When building Qt, qt_build_config.prf adds all directory variables but
DESTDIR to QMAKE_DIR_REPLACE_SANE. We must not add the content of
QMAKE_DIR_REPLACE_SANE unconditionally to QMAKE_DIR_REPLACE in order
to avoid duplicate entries.

Duplicate entries result in an interesting build folder structure like

.obj
├───debug
│   └───debug
└───release
    └───release

This commit amends 274882a5.

Change-Id: Ifa8178410d82f58635babc46d43774bab522fbf8
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

mkspecs/features/exclusive_builds.prf

@@ -37,6 +37,9 @@ defineTest(addExclusiveBuilds) {
     addExclusiveBuildsProper($$join(ARGS, _and_), $$ARGS)
 }
 
-# Default directories to process
-QMAKE_DIR_REPLACE_SANE += QGLTF_DIR TRACEGEN_DIR QMLCACHE_DIR LRELEASE_DIR LEX_DIR YACC_DIR
-QMAKE_DIR_REPLACE = OBJECTS_DIR MOC_DIR RCC_DIR PRECOMPILED_DIR DESTDIR $$QMAKE_DIR_REPLACE_SANE
+QMAKE_DEFAULT_DIRS_TO_PROCESS = QGLTF_DIR TRACEGEN_DIR QMLCACHE_DIR LRELEASE_DIR LEX_DIR YACC_DIR
+QMAKE_DIR_REPLACE_SANE += $$QMAKE_DEFAULT_DIRS_TO_PROCESS
+QMAKE_DIR_REPLACE = \
+    OBJECTS_DIR MOC_DIR RCC_DIR PRECOMPILED_DIR DESTDIR \
+    $$QMAKE_DEFAULT_DIRS_TO_PROCESS
+unset(QMAKE_DEFAULT_DIRS_TO_PROCESS)