refactored 32/64bit detection in qmake files to avoid duplication

src/xbus/xbus.pro

@@ -27,46 +27,17 @@ linux:DEFINES += LIN
 macx:DEFINES += APL
 
 # X-Plane plugins must follow a prescribed filename and directory structure.
-# CPU architecture detection copied from externals.pri;
-# TODO: refactor so detection is is done in only one place.
 TARGET_EXT = .xpl
 win32:TARGET = win
 linux:TARGET = lin
 macx:TARGET = mac
-win32:contains(QMAKE_TARGET.arch, x86_64) {
-    DESTDIR = ../../xbus/64
-}
-win32:contains(QMAKE_TARGET.arch, x86) {
-    DESTDIR = ../../xbus
-}
-win32-g++ {
-    WIN_FIND = $$(SYSTEMROOT)\system32\find
-    MINGW64 = $$system($$QMAKE_CXX -Q --help=target | $$WIN_FIND \"-m64\")
-    contains(MINGW64,[enabled]) {
-        DESTDIR = ../../xbus/64
-    }
-    else {
-        DESTDIR = ../../xbus
-    }
-}
-linux-g++ {
-    GCC64 = $$system($$QMAKE_CXX -Q --help=target | grep m64)
-    contains(GCC64,[enabled]) {
-        DESTDIR = ../../xbus/64
-    }
-    else {
-        DESTDIR = ../../xbus
-    }
-}
-linux-g++-64 {
-    DESTDIR = ../../xbus/64
-}
-linux-g++-32 {
-    DESTDIR = ../../xbus
-}
 macx {
     # a single dylib file contains both 32bit and 64bit binaries
     DESTDIR = ../../xbus
 }
+else {
+    equals(WORD_SIZE,64): DESTDIR = ../../xbus/64
+    equals(WORD_SIZE,32): DESTDIR = ../../xbus
+}
 
 include (../../libraries.pri)