* Have set() and set_quoted() of configuration object work with newlines.
set_quoted() makes the value into a double-quoted string, so let's
assume C-style string, in particular with newlines as "\n".
Also take care of remaining newlines in dump_conf_header(). C or nasm
macros expect single-line values so if the value was multi-line, we
would end up with broken syntax. Appending a backslash at each end of
line make them concat into a single line in both C and nasm format
(note: multi-line macros in nasm are actually possible apparently but
use another format not outputted by current meson code). Also note that
the replacement is done at the end only when dumping the conf as a
header because we cannot assume anything about the format when replacing
variables from an input file (in this case, it should be the dev
responsibility).
* Add unit tests for multiline set() and set_quoted().
Fortran: check for undeclared variables by forcing implicit none everywhere
C/C++: check for unused parameters and return types
removed unused variables from test cases
ci: do missing return and unused arg check with Github Actions