* include/sys/cygwin.h (CW_SETERRNO): Define.

* external.cc (CW_SETERRNO): Implement.
* include/cygwin/version.h: Bump CYGWIN_VERSION_API_MINOR to 192 to reflect the
above change.
* path.cc (path_prefix_p): Treat X: as equivalent to x:.
* mkglobals_h: Remove unneeded #define.
* spawn.cc (spawn_guts): Avoid overly wordy initialization to zero.

winsup/cygwin/include/sys/cygwin.h

@@ -141,7 +141,8 @@ typedef enum
     CW_SYNC_WINENV,
     CW_CYGTLS_PADSIZE,
     CW_SET_DOS_FILE_WARNING,
-    CW_SET_PRIV_KEY
+    CW_SET_PRIV_KEY,
+    CW_SETERRNO
   } cygwin_getinfo_types;
 
 #define CW_NEXTPID	0x80000000	/* or with pid to get next one */