Make it possible to disable Qt type pack handlers at build time

usable with either
  qmake DEFINES+=MSGPACK_NO_PACKTYPES
or
  DEFINES += MSGPACK_STATIC MSGPACK_NO_PACKTYPES
  include(path/to/qmsgpack/qmsgpack.pri)

qmsgpack.pri

@@ -7,10 +7,7 @@ SOURCES += \
     $$PWD/src/msgpackcommon.cpp \
     $$PWD/src/private/pack_p.cpp \
     $$PWD/src/private/unpack_p.cpp \
-    $$PWD/src/private/qt_types_p.cpp \
-    $$PWD/src/msgpackstream.cpp \
-    $$PWD/src/stream/time.cpp \
-    $$PWD/src/stream/geometry.cpp
+    $$PWD/src/msgpackstream.cpp
 
 HEADERS += \
     $$PWD/src/msgpack.h \
@@ -19,18 +16,27 @@ HEADERS += \
     $$PWD/src/endianhelper.h \
     $$PWD/src/msgpackcommon.h \
     $$PWD/src/msgpack_export.h \
-    $$PWD/src/private/qt_types_p.h \
-    $$PWD/src/msgpackstream.h \
-    $$PWD/src/stream/time.h \
-    $$PWD/src/stream/geometry.h
+    $$PWD/src/msgpackstream.h
 
-qtHaveModule(gui) {
-    QT += gui
-}
+!contains(DEFINES, MSGPACK_NO_PACKTYPES) {
+    SOURCES += \
+        $$PWD/src/private/qt_types_p.cpp \
+        $$PWD/src/stream/time.cpp \
+        $$PWD/src/stream/geometry.cpp
 
-qtHaveModule(location) {
-    QT += location
+    HEADERS += \
+        $$PWD/src/private/qt_types_p.h \
+        $$PWD/src/stream/time.h \
+        $$PWD/src/stream/geometry.h
 
-    SOURCES += $$PWD/src/stream/location.cpp
-    HEADERS += $$PWD/src/stream/location.h
+    qtHaveModule(gui) {
+        QT += gui
+    }
+
+    qtHaveModule(location) {
+        QT += location
+
+        SOURCES += $$PWD/src/stream/location.cpp
+        HEADERS += $$PWD/src/stream/location.h
+    }
 }