5.15.y backport request to fix compilation error in selftests/kvm

[Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>]

Hi,

On arm machine we have a compilation error while building 
tools/testing/selftests/kvm/ with LTS 5.15.y kernel

rseq_test.c: In function ‘main’:
rseq_test.c:236:33: warning: implicit declaration of function ‘gettid’; 
did you mean ‘getgid’? [-Wimplicit-function-declaration]
           (void *)(unsigned long)gettid());
                                  ^~~~~~
                                  getgid
/tmp/cc4Wfmv2.o: In function `main':
/home/test/linux/tools/testing/selftests/kvm/rseq_test.c:236: undefined 
reference to `gettid'
collect2: error: ld returned 1 exit status
make: *** [../lib.mk:151: 
/home/test/linux/tools/testing/selftests/kvm/rseq_test] Error 1
make: Leaving directory '/home/test/linux/tools/testing/selftests/kvm'


This is fixed by commit 561cafebb2cf97b0927b4fb0eba22de6200f682e upstream.
Kernel version to apply: 5.15.y LTS

Could we please backport the above fix onto 5.15.y LTS. It applies 
cleanly and the kvm selftests compile properly after applying the patch.

Liam pointed the same in [1]

Thanks,
Harshit

[1] 
https://lore.kernel.org/all/fdfb143a-45c4-aaff-aa95-d20c076ff555@oracle.com/