#ifdef __cplusplus missing in tracking_cpu_stats.h

[ghost]

Describe the bug
When we include the header file subsys/tracing/include/tracing_cpu_stats.h
into the C++ file with reference to one of the functions it will not link.

To Reproduce
Steps to reproduce the behavior:

1. add C++ file into the Zephyr project
2. enable TRACING_CPU_STATS in menuconfig
3. #include "tracing_cpu_stats.h"
4. call on of the functions, e.g. cpu_stats_non_idle_and_sched_get_percent();
5. compile and see the error

Expected behavior
The project should compile and link.

Impact
The feature prevent from compiling the project.

Screenshots or console output
: app/libapp.a(cpu_detailed_stats.cpp.obj): in function saveData': /home/hid/aurora/aurora/app/src/cpu_stats/cpu_detailed_stats.cpp:169: undefined reference to cpu_stats_non_idle_and_sched_get_percent()'
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld: /home/hid/aurora/aurora/app/src/cpu_stats/cpu_detailed_stats.cpp:171: undefined reference to `cpu_stats_reset_counters()'
collect2: error: ld returned 1 exit status

Environment (please complete the following information):

• OS: Linux
• Toolchain ninja
• Version 2.2.0.0

Additional context
The fix is to add the following #ifdefs into the header file:

diff --git a/subsys/tracing/include/tracing_cpu_stats.h b/subsys/tracing/include/tracing_cpu_stats.h
index cacaad21e0..4c5c2d23a9 100644
--- a/subsys/tracing/include/tracing_cpu_stats.h
+++ b/subsys/tracing/include/tracing_cpu_stats.h
@@ -10,6 +10,10 @@
#include <kernel_structs.h>
#include <init.h>

+#ifdef __cplusplus
+extern "C" {
+#endif
+
struct cpu_stats {
u64_t idle;
u64_t non_idle;
@@ -41,4 +45,8 @@ void cpu_stats_reset_counters(void);
#define sys_trace_void(id)
#define sys_trace_end_call(id)

+#ifdef __cplusplus
+}
+#endif
+
#endif /* _TRACE_CPU_STATS_H */

[ioannisg]

thanks for this bug report -
would it be possible to provide a fix PR @dlisik-hid ?