package/meson: fix malformed cross-compilation.conf.in

package/meson: fix malformed cross-compilation.conf.in

Currently, meson will set the c_link_args and the cpp_link_args to the
value of TARGET_LDFLAGS, even when it's not defined.

This creates a malformed array ["",] which will break any package
building using meson/ninja.

We fix that by using an empty replacement when the corresponding values
are empty.

Reported-by: Adam Duskett <Adamduskett@outlook.com>
Signed-off-by: Adam Duskett <Adamduskett@outlook.com>
[yann.morin.1998@free.fr: alternate implementation, suggested by Thomas]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Adam Duskett aduskett@gmail.com
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>