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

173ef8980d build: Small libxcb.mk improvements (Hennadii Stepanov)
5129b36573 build: Clean remnants of QTBUG-34748 fix (Hennadii Stepanov)

Pull request description:

  Hope, this PR will make [transit](https://github.com/bitcoin/bitcoin/pull/21376) to Qt 5.12.10 neater.

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

  [QTBUG-34748](https://bugreports.qt.io/browse/QTBUG-34748) was [fixed](b19b080894) in Qt 5.3.0.

  The separated [`fix-xcb-include-order.patch`](bb44d9e754/depends/patches/qt/fix-xcb-include-order.patch), provided by #5915, was dropped in #12971 while bumping Qt to 5.9.4 (5.9.6). But `libxcb.mk` remained unchanged.

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

ACKs for top commit:
  practicalswift:
    cr ACK 173ef8980d: patch looks correct
  fanquake:
    ACK 173ef8980d

Tree-SHA512: 9815a7e532ff4aa08f9623ded8d5708eca1c9c73ac7a2684419a18c125da7627b44ac3191f2e7978946942c8d0580e73b1a93df624986fb2a13791a68ce1e025

depends/packages/libxcb.mk

@@ -27,13 +27,8 @@ define $(package)_preprocess_cmds
   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