cpupower: avoid multiple definition with gcc -fno-common

cpupower: avoid multiple definition with gcc -fno-common

[ Upstream commit 2de7fb60a4740135e03cf55c1982e393ccb87b6b ]

Building cpupower with -fno-common in CFLAGS results in errors due to
multiple definitions of the 'cpu_count' and 'start_time' variables.

./utils/idle_monitor/snb_idle.o:./utils/idle_monitor/cpupower-monitor.h:28:
multiple definition of `cpu_count';
./utils/idle_monitor/nhm_idle.o:./utils/idle_monitor/cpupower-monitor.h:28:
first defined here
...
./utils/idle_monitor/cpuidle_sysfs.o:./utils/idle_monitor/cpuidle_sysfs.c:22:
multiple definition of `start_time';
./utils/idle_monitor/amd_fam14h_idle.o:./utils/idle_monitor/amd_fam14h_idle.c:85:
first defined here

The -fno-common option will be enabled by default in GCC 10.

Bug: https://bugs.gentoo.org/707462
Signed-off-by: Mike Gilbert <floppym@gentoo.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>