Support POSIX basename() from musl libc (#123)

Musl libc 1.2.5 removed the definition of the basename() function from
string.h and only provides it in libgen.h as the POSIX standard
defines it.

This change fixes compilation with musl libc 1.2.5.
````
build_dir/target-mips_24kc_musl/rtty-mbedtls/rtty-8.1.1/src/file.c:156:24: error: implicit declaration of function 'basename' [-Werror=implicit-function-declaration]
  156 |     const char *name = basename(path);
      |                        ^~~~~~~~
````

basename() modifies the input string, copy it first with strdup(), If
strdup() returns NULL the code will handle it.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

src/file.c

@@ -29,6 +29,7 @@
 #include <unistd.h>
 #include <mntent.h>
 #include <inttypes.h>
+#include <libgen.h>
 #include <sys/statvfs.h>
 #include <linux/limits.h>
 #include <sys/sysinfo.h>
@@ -153,13 +154,17 @@ static int start_upload_file(struct file_context *ctx, const char *path)
 {
     struct tty *tty = container_of(ctx, struct tty, file);
     struct rtty *rtty = tty->rtty;
-    const char *name = basename(path);
+    const char *name;
     struct stat st;
     int fd;
+    char *dirc;
 
+    dirc = strdup(path);
+    name = basename(dirc);
     fd = open(path, O_RDONLY);
     if (fd < 0) {
         log_err("open '%s' fail: %s\n", path, strerror(errno));
+        free(dirc);
         return -1;
     }
 
@@ -177,6 +182,7 @@ static int start_upload_file(struct file_context *ctx, const char *path)
     ctx->remain_size = st.st_size;
 
     log_info("upload file: %s, size: %" PRIu64 "\n", path, (uint64_t)st.st_size);
+    free(dirc);
 
     return 0;
 }

src/filectl.c

@@ -30,6 +30,7 @@
 #include <errno.h>
 #include <stdio.h>
 #include <fcntl.h>
+#include <libgen.h>
 
 #include "utils.h"
 #include "file.h"
@@ -75,6 +76,7 @@ static void handle_file_control_msg(int fd, int sfd, const char *path)
 {
     struct file_control_msg msg;
     struct buffer b = {};
+    char *dirc;
 
     while (true) {
         if (buffer_put_fd(&b, fd, -1, NULL) < 0)
@@ -90,7 +92,9 @@ static void handle_file_control_msg(int fd, int sfd, const char *path)
             if (sfd > -1) {
                 close(sfd);
                 gettimeofday(&start_time, NULL);
-                printf("Transferring '%s'...Press Ctrl+C to cancel\n", basename(path));
+                dirc = strdup(path);
+                printf("Transferring '%s'...Press Ctrl+C to cancel\n", basename(dirc));
+                free(dirc);
 
                 if (total_size == 0) {
                     printf("  100%%    0 B     0s\n");