Actually enable the windows absolute-path code

Checking for "WINDOWS" is wrong; our magic macro is MS_WINDOWS

Fixes bug 4973; bugfix on 0.2.3.11-alpha.

changes/bug4973

@@ -0,0 +1,3 @@
+  o Minor bugfixes:
+    - Calculate absolute paths correctly on Windows. Fixes bug 4973;
+      bugfix on 0.2.3.11-alpha.

src/common/compat.c

@@ -1628,7 +1628,7 @@ get_parent_directory(char *fname)
 char *
 make_path_absolute(char *fname)
 {
-#ifdef WINDOWS
+#ifdef MS_WINDOWS
   char *absfname_malloced = _fullpath(NULL, fname, 1);
 
   /* We don't want to assume that tor_free can free a string allocated