Fix libpcsclite.pc fiel generated by Meson

[arrowd]

Running pkgconf --libs --cflags does not include -pthread without this change. It also matches what the autotools build generates.

The issue was brought up in FreeBSD Ports: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=285857#c3

[LudovicRousseau]

The generated libpcsclite.pc file already includes -pthread in the Libs.private: field:

Name: PCSC Lite
Description: PC/SC smart card interface
Version: 2.3.2
Libs: -L${libdir} -lpcsclite
Libs.private: -pthread
Cflags: -I${includedir}/PCSC

It is the same configuration as I used with autotools.
https://github.com/LudovicRousseau/PCSC/blob/master/src/libpcsclite.pc.in#L12

If is was working before it should continue to work with the file generated by meson.

From pkg-config manpage https://linux.die.net/man/1/pkg-config

Libs.private:
This line should list any private libraries in use. Private libraries are libraries which are not exposed through your library, but are needed in the case of static linking.

[arrowd]

I'm saying that the pkgconf --libs --cflags command output does not have -pthread without my change.

The autotools variant has @PTHREAD_CFLAGS@ in the Cflags field, which ends up being replaced with -pthread.

[LudovicRousseau]

Exact. I missed the Cflags field.

Thanks for the patch.