meson.build: default to -gsplit-dwarf for debug info

meson.build: default to -gsplit-dwarf for debug info

This option is supported by both gcc (since 4.7) and clang (since
7.0). Not only does this make the linkers job easier by reducing the
amount of ELF it needs to parse it also reduces the total build size
quite considerably. In my case a default build went from 5.8G to
3.9G (vs 1.9G for --disable-debug-info).

The --disable-split-debug option allows distros to keep all the info
together for ease of packaging.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Link: https://lore.kernel.org/r/20250306161631.2477685-1-alex.bennee@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>