selftests/bpf: Fix set but not used errors

tools/testing/selftests/bpf/map_tests/lpm_trie_map_basic_ops.c

@@ -226,7 +226,8 @@ static void test_lpm_order(void)
 static void test_lpm_map(int keysize)
 {
 	LIBBPF_OPTS(bpf_map_create_opts, opts, .map_flags = BPF_F_NO_PREALLOC);
-	volatile size_t n_matches, n_matches_after_delete;
+	/* To avoid a -Wunused-but-set-variable warning. */
+	__maybe_unused volatile size_t n_matches, n_matches_after_delete;
 	size_t i, j, n_nodes, n_lookups;
 	struct tlpm_node *t, *list = NULL;
 	struct bpf_lpm_trie_key_u8 *key;

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

@@ -423,7 +423,8 @@ static void tp_subtest(struct test_bpf_cookie *skel)
 
 static void burn_cpu(void)
 {
-	volatile int j = 0;
+	/* To avoid a -Wunused-but-set-variable warning. */
+	__maybe_unused volatile int j = 0;
 	cpu_set_t cpu_set;
 	int i, err;
 

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

@@ -49,7 +49,8 @@ static bool find_vma_pe_condition(struct find_vma *skel)
 static void test_find_vma_pe(struct find_vma *skel)
 {
 	struct bpf_link *link = NULL;
-	volatile int j = 0;
+	/* To avoid a -Wunused-but-set-variable warning. */
+	__maybe_unused volatile int j = 0;
 	int pfd, i;
 	const int one_bn = 1000000000;
 

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

@@ -64,7 +64,8 @@ static void test_perf_branches_common(int perf_fd,
 	int err, i, duration = 0;
 	bool detached = false;
 	struct bpf_link *link;
-	volatile int j = 0;
+	/* To avoid a -Wunused-but-set-variable warning. */
+	__maybe_unused volatile int j = 0;
 	cpu_set_t cpu_set;
 
 	skel = test_perf_branches__open_and_load();

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

@@ -12,7 +12,8 @@
 
 static void burn_cpu(void)
 {
-	volatile int j = 0;
+	/* To avoid a -Wunused-but-set-variable warning. */
+	__maybe_unused volatile int j = 0;
 	cpu_set_t cpu_set;
 	int i, err;
 

tools/testing/selftests/bpf/test_maps.h

@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdbool.h>
+#include <linux/compiler.h>
 
 #define CHECK(condition, tag, format...) ({				\
 	int __ret = !!(condition);					\

tools/testing/selftests/bpf/test_progs.h

@@ -16,6 +16,7 @@
 #include <linux/types.h>
 typedef __u16 __sum16;
 #include <arpa/inet.h>
+#include <linux/compiler.h>
 #include <linux/if_ether.h>
 #include <linux/if_packet.h>
 #include <linux/ip.h>