Fix -Wpointer-to-int-cast warning in test_api_seap_concurency.c
Fix -Wpointer-to-int-cast warning in test_api_seap_concurency.c

Glibc's pthread_self() returns an unsigned long, and FreeBSD's libc
returns a pointer to a struct pthread. In both cases the value may be
truncated when cast to an unsigned int. Fix this by casting the result
of pthread_self() to a uintptr_t.

OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap