package/pkg-meson.mk: refactor flags substitution with make-comma-list

package/pkg-meson.mk: refactor flags substitution with make-comma-list

pkg-meson defines variables _MESON_SED_CFLAGS, _MESON_SED_LDFLAGS and
_MESON_SED_CXXFLAGS that reformat the make-style flags (space-separated
and unquoted) as meson-style flags (comma-separated and double-quoted).
Similar variables are also defined in meson.mk. A future patch will add
even more similar cases.

However, we already have a macro that does something similar for
generating JSON output: make-comma-list. So let's use that. However,
make-comma-list doesn't add all the shell-expanded magic like
_MESON_SED_CFLAGS, which results in the double quotes being removed by
the shell. Therefore, we also need to change the quoting around it to
single quotes instead of double quotes. For consistency, the quotes of
the other sed expressions are changed as well. Except for the
_MESON_EXTRA_BINARIES: the values set by packages (e.g. mesa3d) already
contain single quotes, so changing the surrounding double quotes to
single quotes would break them.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[yann.morin.1998@free.fr: slight fix in commit log]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>