system/qtest: Replace sprintf by qemu_hexdump_line

sprintf() is deprecated on Darwin since macOS 13.0 / XCode 14.1.
Using qemu_hexdump_line both fixes the deprecation warning and
simplifies the code base.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>`
[rth: Use qemu_hexdump_line]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20240412073346.458116-8-richard.henderson@linaro.org>
diff --git a/system/qtest.c b/system/qtest.c
index 6da58b3..507a358 100644
--- a/system/qtest.c
+++ b/system/qtest.c
@@ -601,9 +601,9 @@
         qtest_send_prefix(chr);
         qtest_sendf(chr, "OK 0x%016" PRIx64 "\n", value);
     } else if (strcmp(words[0], "read") == 0) {
-        uint64_t addr, len, i;
+        g_autoptr(GString) enc = NULL;
+        uint64_t addr, len;
         uint8_t *data;
-        char *enc;
         int ret;
 
         g_assert(words[1] && words[2]);
@@ -618,16 +618,12 @@
         address_space_read(first_cpu->as, addr, MEMTXATTRS_UNSPECIFIED, data,
                            len);
 
-        enc = g_malloc(2 * len + 1);
-        for (i = 0; i < len; i++) {
-            sprintf(&enc[i * 2], "%02x", data[i]);
-        }
+        enc = qemu_hexdump_line(NULL, data, len, 0, 0);
 
         qtest_send_prefix(chr);
-        qtest_sendf(chr, "OK 0x%s\n", enc);
+        qtest_sendf(chr, "OK 0x%s\n", enc->str);
 
         g_free(data);
-        g_free(enc);
     } else if (strcmp(words[0], "b64read") == 0) {
         uint64_t addr, len;
         uint8_t *data;