perf: improve fixing for buildpaths QA warning

perf: improve fixing for buildpaths QA warning

if O=${B} is removed from EXTRA_OEMAKE, perf will compile failed with
error:
| make[2]: *** No rule to make target 'tools/arch/arm64/include/uapi/asm/unistd.h', needed by 'arch/arm64/include/generated/asm/syscalls.c'.  Stop.

Improve to add an extra rel_sysdef for fixing buildpaths QA warning,
and keep original sysdef

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>