Libs
@PTHREAD_CFLAGS@
That should be only on the CFlags. When using the compiler as the linker driver, one may want to also call pkg-config to get the cflags, but when invoking the linker, there should be no compiler flags.
The referenced bug was fixed in 2007 and has been released in pkg-config-0.23 (16.Jan.2008). The fixed version is widely available.