Backport trunk's r45715:

Define MAXPATHLEN to be at least PATH_MAX, if that's defined. Python uses
MAXPATHLEN-sized buffers for various output-buffers (like to realpath()),
and that's correct on BSD platforms, but not Linux (which uses PATH_MAX, and
does not define MAXPATHLEN.) Cursory googling suggests Linux is following a
newer standard than BSD, but in cases like this, who knows. Using the
greater of PATH_MAX and 1024 as a fallback for MAXPATHLEN seems to be the
most portable solution.

Python/getcwd.c

@@ -14,8 +14,12 @@
 #endif
 
 #ifndef MAXPATHLEN
+#if defined(PATH_MAX) && PATH_MAX > 1024
+#define MAXPATHLEN PATH_MAX
+#else
 #define MAXPATHLEN 1024
 #endif
+#endif
 
 extern char *getwd(char *);