proc: test last field of /proc/loadavg

Test fork counter formerly known as ->last_pid, the only part of /proc/loadavg which can be tested.

Testing in init pid namespace is not reliable because of background activity.

---

 tools/testing/selftests/proc/.gitignore         |    1 
 tools/testing/selftests/proc/Makefile           |    1 
 tools/testing/selftests/proc/proc-loadavg-001.c |   83 ++++++++++++++++++++++++
 3 files changed, 85 insertions(+)

@@ -1,3 +1,4 @@
+/proc-loadavg-001
 /proc-self-map-files-001
 /proc-self-map-files-002
 /proc-self-syscall

@@ -1,6 +1,7 @@
 CFLAGS += -Wall -O2
 
 TEST_GEN_PROGS :=
+TEST_GEN_PROGS += proc-loadavg-001
 TEST_GEN_PROGS += proc-self-map-files-001
 TEST_GEN_PROGS += proc-self-map-files-002
 TEST_GEN_PROGS += proc-self-syscall

new file mode 100644