DT_UNKNOWN: do not fully trust existence of DT_UNKNOWN

The recent Cygwin defines DT_UNKNOWN although it does not have d_type
in struct dirent.  Give an option to tell us not to use d_type on such
platforms.  Hopefully this problem will be transient.

Signed-off-by: Junio C Hamano <junkio@cox.net>

Makefile

@@ -21,6 +21,9 @@ all:
 #
 # Define NO_D_INO_IN_DIRENT if you don't have d_ino in your struct dirent.
 #
+# Define NO_D_TYPE_IN_DIRENT if your platform defines DT_UNKNOWN but lacks
+# d_type in struct dirent (latest Cygwin -- will be fixed soonish).
+#
 # Define NO_STRCASESTR if you don't have strcasestr.
 #
 # Define NO_SETENV if you don't have setenv in the C library.
@@ -236,6 +239,7 @@ ifeq ($(uname_S),SunOS)
 	ALL_CFLAGS += -D__EXTENSIONS__
 endif
 ifeq ($(uname_O),Cygwin)
+	NO_D_TYPE_IN_DIRENT = YesPlease
 	NO_D_INO_IN_DIRENT = YesPlease
 	NO_STRCASESTR = YesPlease
 	NEEDS_LIBICONV = YesPlease
@@ -337,6 +341,9 @@ ifdef NEEDS_NSL
 	LIBS += -lnsl
 	SIMPLE_LIB += -lnsl
 endif
+ifdef NO_D_TYPE_IN_DIRENT
+	ALL_CFLAGS += -DNO_D_TYPE_IN_DIRENT
+endif
 ifdef NO_D_INO_IN_DIRENT
 	ALL_CFLAGS += -DNO_D_INO_IN_DIRENT
 endif

cache.h

@@ -10,7 +10,7 @@
 #define deflateBound(c,s)  ((s) + (((s) + 7) >> 3) + (((s) + 63) >> 6) + 11)
 #endif
 
-#ifdef DT_UNKNOWN
+#if defined(DT_UNKNOWN) && !NO_D_TYPE_IN_DIRENT
 #define DTYPE(de)	((de)->d_type)
 #else
 #define DT_UNKNOWN	0