meson: reformat default options to workaround bug in `meson configure`
Since 13cb20fc46 ("meson: fix compilation with Visual Studio", 2025-01-22) it has not been possible to list build options via `meson configure`. This is due to Meson's static analysis of build options failing to handle constant folding, and thinking we set a totally invalid default `-std=`. This is reported upstream but we anyways need to work with existing versions. It turns out there is a simple solution: turn the entire default option into a conditional branch, which means Meson sees either nothing, or everything. As a result, Git users can once again see pretty-printed options before building. Reported-by: Ramsay Jones <ramsay@ramsayjones.plus.com> Bug: https://github.com/mesonbuild/meson/issues/14623 Signed-off-by: Eli Schwartz <eschwartz@gentoo.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>