See here for background: https://bugreports.qt.io/browse/QTBUG-34748
libxcb temporarily had an abi breakage which caused crashes when qt was
compiled against a non-compatible version. Building qt with -qt-xcb should have
shielded us from this issue, except that incompatible headers were used when
building qt's wrapper.
Make sure those headers aren't picked up by qt's build.
Details:
qt's build adds a wrapper around the xcb libs when -qt-xcb is used. This is
done to avoid having to link to a handful of different libs, which may not be
api/abi stable. This build depends on include-order, so that its files are
found before the real libxcb headers.
Our build (for other reasons related to qt's complicated build-system) injects
our prefix into CXXFLAGS. Because libxcb is found in this path, that reverses
the include-order, negating the purpose of the wrapper.
To fix, libxcb's includes are simply moved to a subdir. pkg-config ensures that
they're still found properly when needed.
To make things even more interesting, this behavior in qt's .pro files is broken:
INCLUDEPATH += $$QMAKE_CFLAGS_XCB
The INCLUDEPATH variable is processed by qmake which automatically prefixes each
entry with "-I". The QMAKE_CFLAGS_XCB variable comes from pkg-config and
already contains -I, making the path look like "-I-I/path/to/xcb/headers".
To work around that, CFLAGS/CXXFLAGS are used here rather than INCLUDEPATH.
tl;dr: Update to the newer stable toolchain and SDK for OSX without giving up
any backwards compatibility. We can move to clang 3.5 as a next step which
allows use to use libc++ and the 10.10 sdk, but we'll need to find a build that
works in gitian/travis first.
Switch to a new, better maintained fork of cctools:
https://github.com/tpoechtrager/cctools-port
I've forked this and will be working on it some as well:
https://github.com/theuni/cctools-port
This brings in:
cctools v862
ld64: v241.9
It also fixes 64bit builds, so there's no longer any need to use a 32bit clang.
Since clang is no longer tied to an old/crusty 32bit build, clang has been
upgraded to 3.3. Unfortunately, there's a bug in 3.4 that breaks builds. 3.5
works fine, but there are no binary builds compatible with precise, which is
currently used for gitian and travis. We could always build our own if
necessary.
After updating to stable clang/linker/cctools, it's possible to use a more
recent SDK. The current SDK (10.7) through the most recent 10.10 have all been
built/tested successfully, both with and without 10.6 compatibility. However,
10.10 requires clang 3.5.
SDKs >= 10.9 use libc++ rather than libstdc++. This is verified working as well.
