git-count-objects: Fix a disk-space under-estimate on Cygwin

Cygwin has st_blocks in struct stat, but at least on NTFS, the field
counts in blocks of st_blksize bytes, not in 512-byte blocks.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -776,6 +776,7 @@ ifeq ($(uname_O),Cygwin)
 	NO_FAST_WORKING_DIRECTORY = UnfortunatelyYes
 	NO_TRUSTABLE_FILEMODE = UnfortunatelyYes
 	OLD_ICONV = UnfortunatelyYes
+	NO_ST_BLOCKS_IN_STRUCT_STAT = YesPlease
 	# There are conflicting reports about this.
 	# On some boxes NO_MMAP is needed, and not so elsewhere.
 	# Try commenting this out if you suspect MMAP is more efficient