hash.h: set NEEDS_CLONE_HELPER_UNSAFE in fallback mode

Commit 253ed9e (hash.h: scaffolding for _unsafe hashing variants,
2024-09-26) introduced the concept of having two hash algorithms: a safe
and an unsafe one. When the Makefile knobs do not explicitly request an
unsafe one, we fall back to using the safe algorithm.

However, the fallback to do so forgot one case: we should inherit the
NEEDS_CLONE_HELPER flag from the safe variant. Failing to do so means
that we'll end up defining two clone functions (the algorithm specific
one, and the generic one that just calls memcpy). You'll see an error
like this:

  $ make OPENSSL_SHA1=1
  [...]
  sha1/openssl.h:46:29: error: redefinition of ‘openssl_SHA1_Clone’
     46 | #define platform_SHA1_Clone openssl_SHA1_Clone
        |                             ^~~~~~~~~~~~~~~~~~
  hash.h:83:40: note: in expansion of macro ‘platform_SHA1_Clone’
     83 | #    define platform_SHA1_Clone_unsafe platform_SHA1_Clone
        |                                        ^~~~~~~~~~~~~~~~~~~
  hash.h:101:33: note: in expansion of macro ‘platform_SHA1_Clone_unsafe’
    101 | #  define git_SHA1_Clone_unsafe platform_SHA1_Clone_unsafe
        |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~
  hash.h:133:20: note: in expansion of macro ‘git_SHA1_Clone_unsafe’
    133 | static inline void git_SHA1_Clone_unsafe(git_SHA_CTX_unsafe *dst,
        |                    ^~~~~~~~~~~~~~~~~~~~~
  sha1/openssl.h:37:20: note: previous definition of ‘openssl_SHA1_Clone’ with type ‘void(struct openssl_SHA1_CTX *, const struct openssl_SHA1_CTX *)’
     37 | static inline void openssl_SHA1_Clone(struct openssl_SHA1_CTX *dst,
        |                    ^~~~~~~~~~~~~~~~~~

This only matters when compiling with openssl as the "safe" variant,
since it's the only algorithm that requires a clone helper (and even
then, only if you are using openssl 3.0+). And you should never do that,
because it's not safe. But still, the invocation above used to work and
should continue to do so until we decide to require a
collision-detecting variant for the safe algorithm entirely.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

hash.h

@@ -82,6 +82,9 @@
 #  ifdef platform_SHA1_Clone
 #    define platform_SHA1_Clone_unsafe platform_SHA1_Clone
 #  endif
+#  ifdef SHA1_NEEDS_CLONE_HELPER
+#    define SHA1_NEEDS_CLONE_HELPER_UNSAFE
+#  endif
 #endif
 
 #define git_SHA_CTX		platform_SHA_CTX