selftests/bpf: Declare bpf_log_buf variables as static

The cgroup selftests did not declare the bpf_log_buf variable as static, leading
to a linker error with GCC 10 (which defaults to -fno-common). Fix this by
adding the missing static declarations.

Fixes: 257c8855 ("selftests/bpf: Convert test_cgroup_attach to prog_tests")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrey Ignatov <rdna@fb.com>
Link: https://lore.kernel.org/bpf/20200302145348.559177-1-toke@redhat.com

tools/testing/selftests/bpf/prog_tests/cgroup_attach_autodetach.c

@@ -6,7 +6,7 @@
 
 #define PING_CMD	"ping -q -c1 -w1 127.0.0.1 > /dev/null"
 
-char bpf_log_buf[BPF_LOG_BUF_SIZE];
+static char bpf_log_buf[BPF_LOG_BUF_SIZE];
 
 static int prog_load(void)
 {

tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c

@@ -6,7 +6,7 @@
 
 #define PING_CMD	"ping -q -c1 -w1 127.0.0.1 > /dev/null"
 
-char bpf_log_buf[BPF_LOG_BUF_SIZE];
+static char bpf_log_buf[BPF_LOG_BUF_SIZE];
 
 static int map_fd = -1;
 

tools/testing/selftests/bpf/prog_tests/cgroup_attach_override.c

@@ -8,7 +8,7 @@
 #define BAR		"/foo/bar/"
 #define PING_CMD	"ping -q -c1 -w1 127.0.0.1 > /dev/null"
 
-char bpf_log_buf[BPF_LOG_BUF_SIZE];
+static char bpf_log_buf[BPF_LOG_BUF_SIZE];
 
 static int prog_load(int verdict)
 {