Using variadic macros like `qCWarning()` without any parameter for "..."
is a GNU extension, which causes a lot of `clang` warnings:
```
desktop/src/common/ownsql.cpp:74:24: warning: must specify at least one
argument for '...' parameter of variadic macro
[-Wgnu-zero-variadic-macro-arguments]
qCWarning(lcSql) << "Error:" << _error << "for" << filename;
^
/usr/include/qt/QtCore/qloggingcategory.h:140:11: note: macro 'qCWarning'
defined here
^
```
This patch tells `clang` to be silent.
Signed-off-by: Johannes Lorenz <j.git@lorenz-ho.me>
