nptl: Add NPTL cases for cancellation failures cases

This patch pthread cancellation tests to check for failures cases
wherer the syscall cancel wrapper should both set the error and
the errno values.

Tested on i686, x86_64, x32, powerpc64le, and aarch64.

	* nptl/Makefile (tests): Add tst-cancel26.c and tst-cancel27.c.
	* nptl/tst-cancel26.c: New file.
	* nptl/tst-cancel27.c: Likewise.