Gwenhywfar

build: fixed handling of libdl.

For some unknown reason autoconf is test-compiling C++ code with gcc
instead of g++. This change forces the use C code with a C compiler.

Support out-of-source build for Qt6 gui

Prepared release 5.12.1

Added missing symlink for Qt6

Support building for Qt6

Remove debug output

Improve configuration on systems with Qt5 and Qt6 installed

Prevent configuration for Qt5 and Qt6 at the same time

Add missing files to AC_CONFIG_FILES

Adjusted expression to work correclty using Qt5 and Qt6

nogui: fixed a bug.

returning 1 completely disables logging in NOGUI module which isn't exactly
what's intended; we don't want console output by NOGUI, but we don't want
to suppress logs to files or syslog.

logger: don't open already opened logger.

Support building for Qt6

Fix name of output variable

inetsocket: added flags (for raw dumping).

tag16: added some tag read/write functions.

added GWEN_Timestamp_GetWeekDay()

Remove double declaration of HtmlObject_Grid_new

This fixes a build failure when compiling with GCC 15 due to conflicting
declarations of HtmlObject_Grid_new.

The build failure was initially reported by Matthias Klose <doko@debian.org> as
Debian bug https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1097194

Fix compilation under MacOS

Released 5.12.0

Prepared release 5.12.0

msgio: add argument REASON to GWEN_MsgRequest_Abort()

msgio: add class GWEN_REQUEST.

msgio/endpoint: added reference counter.

timestamp: added GWEN_Timestamp_AddSeconds().