Windows: use BLK_SHA1 again

Since NO_OPENSSL is no longer defined on Windows, BLK_SHA1 is not defined
anymore implicitly. Define it explicitly.

As a nice side-effect, we no longer link against libcrypto.dll, which has
non-trivial startup costs because it depends on 6 otherwise unneeded
DLLs.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -911,6 +911,7 @@ ifdef MSVC
 	NO_REGEX = YesPlease
 	NO_CURL = YesPlease
 	NO_PTHREADS = YesPlease
+	BLK_SHA1 = YesPlease
 
 	CC = compat/vcbuild/scripts/clink.pl
 	AR = compat/vcbuild/scripts/lib.pl
@@ -960,6 +961,7 @@ ifneq (,$(findstring MINGW,$(uname_S)))
 	UNRELIABLE_FSTAT = UnfortunatelyYes
 	OBJECT_CREATION_USES_RENAMES = UnfortunatelyNeedsTo
 	NO_REGEX = YesPlease
+	BLK_SHA1 = YesPlease
 	COMPAT_CFLAGS += -D__USE_MINGW_ACCESS -DNOGDI -Icompat -Icompat/fnmatch
 	COMPAT_CFLAGS += -DSTRIP_EXTENSION=\".exe\"
 	COMPAT_OBJS += compat/mingw.o compat/fnmatch/fnmatch.o compat/winansi.o