helper/log: Fix build using _DEBUG_FREE_SPACE_

The glibc API 'mallinfo' is deprecated and the new 'mallinfo2'
should be used from glibc 2.33 (2021-02-01).

Throw an error when '--enable-malloc-logging' is used on systems
that compile without glibc.
Detect the glibc version and, for backward compatibility, define
'mallinfo2' as the old 'mallinfo'. Define a macro for the format
of 'fordblks'.

Change-Id: I68bff7b1b58f0ec2669db0b911f19c1c5a26ed30
Reported-by: Steven J. Hill <steven.hill@konsulko.com>
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8589
Tested-by: jenkins

src/helper/log.c

@@ -30,6 +30,18 @@
 #else
 #error "malloc.h is required to use --enable-malloc-logging"
 #endif
+
+#ifdef __GLIBC__
+#if __GLIBC_PREREQ(2, 33)
+#define FORDBLKS_FORMAT " %zu"
+#else
+/* glibc older than 2.33 (2021-02-01) use mallinfo(). Overwrite it */
+#define mallinfo2 mallinfo
+#define FORDBLKS_FORMAT " %d"
+#endif
+#else
+#error "GNU glibc is required to use --enable-malloc-logging"
+#endif
 #endif
 
 int debug_level = LOG_LVL_INFO;
@@ -105,12 +117,11 @@ static void log_puts(enum log_levels level,
 		/* print with count and time information */
 		int64_t t = timeval_ms() - start;
 #ifdef _DEBUG_FREE_SPACE_
-		struct mallinfo info;
-		info = mallinfo();
+		struct mallinfo2 info = mallinfo2();
 #endif
 		fprintf(log_output, "%s%d %" PRId64 " %s:%d %s()"
 #ifdef _DEBUG_FREE_SPACE_
-			" %d"
+			FORDBLKS_FORMAT
 #endif
 			": %s", log_strings[level + 1], count, t, file, line, function,
 #ifdef _DEBUG_FREE_SPACE_