qt: fix build with zlib for target

This contains a few hacks very specific to Qt's buildsystem. These can be
reverted once we split the build between native and target builds.

Qt's build contains a circular dependency when not using a system zlib.
By far the easiest fix is to switch to a system zlib, rather than Qt's own.
However, that confuses Qt's cross build which assumes that when using a system
zlib, it should also find a system (native) zlib for native tools. The build
breaks if that zlib is not present.

To solve this:
1. Always use a system zlib rather than the one provided by qt
2. Set force_bootstrap, which instructs the build tools to be built as though
   we're cross-compiling (build != target)
3. For build tools, use qt's internal zlib so that a native zlib is not
required.

Step 3 means that if any zlib headers are found by the native build, it will
confuse Qt's internal zlib build. So we also need to make sure that the target
headers/libs aren't found. To do so, specify that our
cflags/cxxflags/cppflags/ldflags only apply for non-host builds.

depends/packages/qt.mk

@@ -140,12 +140,13 @@ define $(package)_preprocess_cmds
   patch -p1 < $($(package)_patch_dir)/pidlist_absolute.patch && \
   patch -p1 < $($(package)_patch_dir)/fix-xcb-include-order.patch && \
   patch -p1 < $($(package)_patch_dir)/fix_qt_pkgconfig.patch && \
-  echo "QMAKE_CFLAGS     += $($(package)_cflags) $($(package)_cppflags)" >> qtbase/mkspecs/common/gcc-base.conf && \
-  echo "QMAKE_CXXFLAGS   += $($(package)_cxxflags) $($(package)_cppflags)" >> qtbase/mkspecs/common/gcc-base.conf && \
-  echo "QMAKE_LFLAGS     += $($(package)_ldflags)" >> qtbase/mkspecs/common/gcc-base.conf && \
-  sed -i.old "s|QMAKE_CFLAGS            = |QMAKE_CFLAGS            = $($(package)_cflags) $($(package)_cppflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
-  sed -i.old "s|QMAKE_LFLAGS            = |QMAKE_LFLAGS            = $($(package)_ldflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
-  sed -i.old "s|QMAKE_CXXFLAGS          = |QMAKE_CXXFLAGS            = $($(package)_cxxflags) $($(package)_cppflags) |" qtbase/mkspecs/win32-g++/qmake.conf
+  echo "!host_build: QMAKE_CFLAGS     += $($(package)_cflags) $($(package)_cppflags)" >> qtbase/mkspecs/common/gcc-base.conf && \
+  echo "!host_build: QMAKE_CXXFLAGS   += $($(package)_cxxflags) $($(package)_cppflags)" >> qtbase/mkspecs/common/gcc-base.conf && \
+  echo "!host_build: QMAKE_LFLAGS     += $($(package)_ldflags)" >> qtbase/mkspecs/common/gcc-base.conf && \
+  sed -i.old "s|QMAKE_CFLAGS            = |!host_build: QMAKE_CFLAGS            = $($(package)_cflags) $($(package)_cppflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
+  sed -i.old "s|QMAKE_LFLAGS            = |!host_build: QMAKE_LFLAGS            = $($(package)_ldflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
+  sed -i.old "s|QMAKE_CXXFLAGS          = |!host_build: QMAKE_CXXFLAGS            = $($(package)_cxxflags) $($(package)_cppflags) |" qtbase/mkspecs/win32-g++/qmake.conf
+
 endef
 
 define $(package)_config_cmds
@@ -153,6 +154,8 @@ define $(package)_config_cmds
   export PKG_CONFIG_LIBDIR=$(host_prefix)/lib/pkgconfig && \
   export PKG_CONFIG_PATH=$(host_prefix)/share/pkgconfig  && \
   ./configure $($(package)_config_opts) && \
+  echo "host_build: QT_CONFIG ~= s/system-zlib/zlib" >> mkspecs/qconfig.pri && \
+  echo "CONFIG += force_bootstrap" >> mkspecs/qconfig.pri && \
   $(MAKE) sub-src-clean && \
   cd ../qttranslations && ../qtbase/bin/qmake qttranslations.pro -o Makefile && \
   cd translations && ../../qtbase/bin/qmake translations.pro -o Makefile && cd ../.. &&\

depends/patches/qt/mac-qmake.conf

@@ -14,10 +14,10 @@ QMAKE_MAC_SDK.macosx.Path = $${MAC_SDK_PATH}
 QMAKE_MAC_SDK.macosx.platform_name = macosx
 QMAKE_MAC_SDK.macosx.SDKVersion = $${MAC_SDK_VERSION}
 QMAKE_MAC_SDK.macosx.PlatformPath = /phony
-QMAKE_CFLAGS += -target $${MAC_TARGET}
-QMAKE_OBJECTIVE_CFLAGS += $$QMAKE_CFLAGS
-QMAKE_CXXFLAGS += $$QMAKE_CFLAGS
-QMAKE_LFLAGS += -target $${MAC_TARGET} -mlinker-version=$${MAC_LD64_VERSION}
+!host_build: QMAKE_CFLAGS += -target $${MAC_TARGET}
+!host_build: QMAKE_OBJECTIVE_CFLAGS += $$QMAKE_CFLAGS
+!host_build: QMAKE_CXXFLAGS += $$QMAKE_CFLAGS
+!host_build: QMAKE_LFLAGS += -target $${MAC_TARGET} -mlinker-version=$${MAC_LD64_VERSION}
 QMAKE_AR = $${CROSS_COMPILE}ar cq
 QMAKE_RANLIB=$${CROSS_COMPILE}ranlib
 QMAKE_LIBTOOL=$${CROSS_COMPILE}libtool