compat/win32: correct for incorrect compiler warning

The 'win build' job of our CI build is failing with the following error:

compat/win32/syslog.c: In function 'syslog':
compat/win32/syslog.c:53:17: error: pointer 'pos' may be used after \
				    'realloc' [-Werror=use-after-free]
   53 |                 memmove(pos + 2, pos + 1, strlen(pos));
    CC compat/poll/poll.o
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compat/win32/syslog.c:47:23: note: call to 'realloc' here
   47 |                 str = realloc(str, st_add(++str_len, 1));
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

However, between this realloc() and the use we have a line that resets
the value of 'pos'. Thus, this error is incorrect. It is likely due to a
new version of the compiler on the CI machines.

Instead of waiting for a new compiler, create a new variable to avoid
this error.

Signed-off-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: derrickstolee

compat/win32/syslog.c

@@ -44,16 +44,17 @@ void syslog(int priority, const char *fmt, ...)
 
 	while ((pos = strstr(str, "%1")) != NULL) {
 		size_t offset = pos - str;
+		char *new_pos;
 		char *oldstr = str;
 		str = realloc(str, st_add(++str_len, 1));
 		if (!str) {
 			free(oldstr);
 			warning_errno("realloc failed");
 			return;
 		}
-		pos = str + offset;
-		memmove(pos + 2, pos + 1, strlen(pos));
-		pos[1] = ' ';
+		new_pos = str + offset;
+		memmove(new_pos + 2, new_pos + 1, strlen(new_pos));
+		new_pos[1] = ' ';
 	}
 
 	switch (priority) {