Add test for getrlimit/setrlimit/prlimit with infinity value

Add test for getrlimit/setrlimit/prlimit with infinity value

Add a test to check that the getrlimit, setrlimit and prlimit functions
and their 64-bit equivalent behave correctly with RLIM_INFINITY and
RLIM64_INFINITY. For that it assumes that the prlimit64 function calls
the syscall directly without translating the value and that the kernel
uses the -1 value to represent infinity.

It first finds a resource with the hard limit set to infinity so the
soft limit can be manipulated easily and check for the consistency
between the value set or get by the prlimit64 and the other functions.

It is Linux specific add it uses the prlimit and prlimit64 functions.

Changelog:
	* sysdeps/unix/sysv/linux/tst-rlimit-infinity.c: New file.
	* sysdeps/unix/sysv/linux/Makefile (tests): Add tst-rlimit-infinity.