fmt v8 currently contains a bug that causes compilation to fail if
`FMT_USE_USER_DEFINED_LITERALS` is defined to 0. This is a regression
from earlier versions. A bug has been filed against fmt:
https://github.com/fmtlib/fmt/issues/2384
MKVToolNix defined this to 0 as earlier fmt versions caused warnings
in their code dealing with user-defined literals with
`-Wpedantic`. Luckily those warnings do not occur with v8 anymore.
The fix is to test in `configure` if the fmt version we're compiling
with is v8 or older, and only to define
`FMT_USE_USER_DEFINED_LITERALS` to 0 for earlier versions.
Fixes#3151.
This is in preparation of fixing #3137. The plan is not to use
libfile's MIME type detection but Qt's. As both mkvmerge and the GUI
need to auto-detect the MIME type, this means that the command line
applications will have to be linked against Qt's core library (but not
the GUI libraries).
I know compilation fails in the multi-precision library with 1.60.0,
the previous requirement. The oldest OS I still support is CentOS 7,
which has 1.69 via EPEL. CentOS 8 is next which comes with 1.66.0, and
that compiles fine. So let's take that as the new baseline.
Prevents using the system qmake6 in cross-compilation situations.
Also cleans up the paths to `lconvert`, `moc`, `rcc` and `uic` from
the Qt 6 detection so that Qt 5 can detect their own version.
Part of the implementation of #3115.
Qt 6
`configure` will look for Qt 6 first and only continue looking for Qt
5 if Qt 6 isn't found or disabled via `--disable-qt6`.
Qt 6 detection works by first looking for the `qmake6` binary. Its location
can be specified with the `--with-qmake6=…` option.
All other Qt 6 related facts (such as compiler & linker flags or the
position of the other required tools such as `lconvert`, `moc`, `rcc` and
`uic`) will be derived from the output generated by `qmake6`.
Note that at this point Qt 6 is not yet supported for the cross-compilation
build to Windows, nor is a static Qt 6 build supported yet.
Note that the command line options `--enable-static-qt`,
`--with-qt-pkg-config-modules` and `--without-qt-pkg-config` only apply to
the Qt 5 and have no effect on Qt 6.
Qt 5
The options for specifying the position of the tools (`--with-moc=…`,
`--with-rcc=…` and `--with-uic=…`) have been removed. Their position
will now be derived from the output generated by `qmake`.
General
Completely disabling the GUI now requires passing both `--disable-qt6`
and `--disable-qt` options.
Part of the implementation of #3115.
