Fix redefinition of PATH_MAX macro with mingw

This fixes the following warning with mingw gcc

blosc-private.h:187: warning: "PATH_MAX" redefined
  187 | #define PATH_MAX MAX_PATH
      |
limits.h:20: note: this is the location of the previous definition
   20 | #define PATH_MAX        260
      |

blosc/blosc-private.h

@@ -184,7 +184,9 @@ extern int g_ntuners;
 
 #if defined(_WIN32)
 #include <windows.h>
+#ifndef PATH_MAX
 #define PATH_MAX MAX_PATH
+#endif
 #define RTLD_LAZY   0x000
 #define popen _popen
 #define pclose _pclose