Boilerplate: Open pipe in binary mode on Windows

Avoids a translation from LF to CRLF, which messes up the
expected byte counts.

Note that popen() on GLibc does not support the 'b' mode,
so this change is for Windows only. From the POSIX.2024
spec:

 > The behavior of popen() is specified for values of mode of "r",
 > "w", "re", and "we". Other modes such as "rb" and "wb" might be
 > supported by specific implementations, but these would not be
 > portable features.

boilerplate/cairo-boilerplate.c

@@ -945,7 +945,11 @@ POPEN:
 
     *close_cb = pclose;
     sprintf (command, "%s %s %d", any2ppm, filename, page);
+#ifndef _WIN32
     return popen (command, "r");
+#else
+    return popen (command, "rb");
+#endif
 }
 
 static cairo_bool_t