perf annotate: Add the cmp_null function and make use of it
perf annotate: Add the cmp_null function and make use of it

This function exists in builtin-report.c but not in
builtin-annotate.c Functions that use cmp_null are shorter and
clearer.

Synchronizing functions between these two files will also make it
easier to potential share code in the future.

Signed-off-by: John Kacur <dae4bd386fd4c6474c13eecbb94aa6e9e7589534@redhat.com>
Cc: Peter Zijlstra <645ca7d3a8d3d4f60557176cd361ea8351edc32b@chello.nl>
LKML-Reference: <deda3546292f417c5732e64332363b3fcda49b57@localhost.localdomain>
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@elte.hu>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs