Merge bitcoin#21382: build: Clean remnants of QTBUG-34748 fix

173ef89 build: Small libxcb.mk improvements (Hennadii Stepanov)
5129b36 build: Clean remnants of QTBUG-34748 fix (Hennadii Stepanov)

Pull request description:

  Hope, this PR will make [transit](bitcoin#21376) to Qt 5.12.10 neater.

  A fix for [QTBUG-34748](https://bugreports.qt.io/browse/QTBUG-34748) was introduced in bitcoin#5915 (v0.11.0, Qt 5.2.1).

  [QTBUG-34748](https://bugreports.qt.io/browse/QTBUG-34748) was [fixed](qt/qtbase@b19b080) in Qt 5.3.0.

  The separated [`fix-xcb-include-order.patch`](https://github.com/theuni/bitcoin/blob/bb44d9e7546e6118cd91db5bbe471a3ce2ee7fcd/depends/patches/qt/fix-xcb-include-order.patch), provided by bitcoin#5915, was dropped in bitcoin#12971 while bumping Qt to 5.9.4 (5.9.6). But `libxcb.mk` remained unchanged.

  This PR reverts bitcoin#5915 for `libxcb.mk` as well.

ACKs for top commit:
  practicalswift:
    cr ACK 173ef89: patch looks correct
  fanquake:
    ACK 173ef89

Tree-SHA512: 9815a7e532ff4aa08f9623ded8d5708eca1c9c73ac7a2684419a18c125da7627b44ac3191f2e7978946942c8d0580e73b1a93df624986fb2a13791a68ce1e025

depends/packages/libxcb.mk

@@ -23,17 +23,12 @@ $(package)_config_opts += --disable-xv --disable-xvmc
 endef
 
 define $(package)_preprocess_cmds
-  cp -f $(BASEDIR)/config.guess $(BASEDIR)/config.sub build-aux &&\
+  cp -f $(BASEDIR)/config.guess $(BASEDIR)/config.sub build-aux && \
   sed "s/pthread-stubs//" -i configure
 endef
 
-# Don't install xcb headers to the default path in order to work around a qt
-# build issue: https://bugreports.qt.io/browse/QTBUG-34748
-# When using qt's internal libxcb, it may end up finding the real headers in
-# depends staging. Use a non-default path to avoid that.
-
 define $(package)_config_cmds
-  $($(package)_autoconf) --includedir=$(host_prefix)/include/xcb-shared
+  $($(package)_autoconf)
 endef
 
 define $(package)_build_cmds
@@ -45,5 +40,5 @@ define $(package)_stage_cmds
 endef
 
 define $(package)_postprocess_cmds
-  rm -rf share/man share/doc lib/*.la
+  rm -rf share lib/*.la
 endef