avoid warning about macro redefinition on Windows + clang: (#44412)

(cherry picked from commit 529ac51)

Author: 2005m

src/support/dirpath.h

@@ -6,14 +6,17 @@
 #ifdef _OS_WINDOWS_
 #define PATHSEPSTRING "\\"
 #define PATHLISTSEPSTRING ";"
+#if defined(PATH_MAX)
 #define JL_PATH_MAX PATH_MAX
-#if defined(_COMPILER_CLANG_)
+#else // _COMPILER_CLANG_ may have the name reversed
 #define JL_PATH_MAX MAX_PATH
 #endif
 #else
 #define PATHSEPSTRING "/"
 #define PATHLISTSEPSTRING ":"
-#ifndef JL_PATH_MAX // many platforms don't have a max path, we define one anyways
+#if defined(PATH_MAX)
+#define JL_PATH_MAX PATH_MAX
+#else // many platforms don't have a max path, we define one anyways
 #define JL_PATH_MAX 1024
 #endif
 #endif