ld64 is threaded, and uses a worker for each CPU to parse input files. But
there's a bug in the parser causing dependencies to be calculated differently
based on which files have already been parsed.
As a result, builders with more CPUs are more likely to see non-determinism.
This looks to have been fixed in a newer version of ld64, so just disable
threading for now. There's no noticible slowdown.
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.
qt5.7 changed the location of some of its symbols, creating a circular
dependency in Qt5Core. Rather than trying to fix that up, build our own zlib
rather than having it built for us.
Their buildsystem insists on using the installed ltranslate, but gets confused
about how to find it. Since we manually control the build order, just drop the
dependency.
Add a patch that seems to be necessary for compatibilty of libevent
2.0.22 with recent mingw-w64 gcc versions (at least GCC 5.3.1 from Ubuntu
16.04).
Without this patch the Content-Length in the HTTP header ends up as
`Content-Length: zu`, causing communication between the RPC
client and server to break down. See discussion in #8653.
Source: https://sourceforge.net/p/levent/bugs/363/
Thanks to @sstone for the suggestion.
Jonas Schnelli