meson: Fix underlinking of static libintl by trying iconv and pthread

I thought about checking for an intl pkg-config file but upstream are not interested in adding one so there seems little point.

I wasn't sure if ngettext was the best function to check for but this seems to be the main function that glib-gettext.m4 checks for.

I fixed this due to QEMU failing to build but it was originally reported as a failure in building the glib tests. I am cross-compiling with mingw-w64 so I cannot run the tests but I was able to build them. @antumdeluge, please could you try this also.

Closes #1851 (closed)