libbpf-tools: Fix compilation error for gethostlatency

Fix the following compilation error with GCC 8.5.0:
    gethostlatency.c: In function ‘attach_uprobes.isra.2’:
    gethostlatency.c:157:58: error: ‘%s’ directive output may be truncated writing up to 4095 bytes into a region of size between 4074 and 4084 [-Werror=format-truncation=]
         snprintf(proc_path, sizeof(proc_path), "/proc/%d/root%s", target_pid, buf);
                                                              ^~               ~~~
    gethostlatency.c:157:5: note: ‘snprintf’ output between 13 and 4118 bytes into a destination of size 4096
         snprintf(proc_path, sizeof(proc_path), "/proc/%d/root%s", target_pid, buf);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    cc1: all warnings being treated as errors

Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>

Author: chenhengqi

libbpf-tools/gethostlatency.c

@@ -124,12 +124,11 @@ static void handle_lost_events(void *ctx, int cpu, __u64 lost_cnt)
 
 static int get_libc_path(char *path)
 {
-	FILE *f;
+	char proc_path[PATH_MAX + 32] = {};
 	char buf[PATH_MAX] = {};
-	char map_fname[PATH_MAX] = {};
-	char proc_path[PATH_MAX] = {};
 	char *filename;
 	float version;
+	FILE *f;
 
 	if (libc_path) {
 		memcpy(path, libc_path, strlen(libc_path));
@@ -139,8 +138,8 @@ static int get_libc_path(char *path)
 	if (target_pid == 0) {
 		f = fopen("/proc/self/maps", "r");
 	} else {
-		snprintf(map_fname, sizeof(map_fname), "/proc/%d/maps", target_pid);
-		f = fopen(map_fname, "r");
+		snprintf(buf, sizeof(buf), "/proc/%d/maps", target_pid);
+		f = fopen(buf, "r");
 	}
 	if (!f)
 		return -errno;