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.
