Configurations: PowerPC is big endian

Define B_ENDIAN on PowerPC because it is a big endian architecture. With
this change the BN* related tests pass.

Fixes: #12199

Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/12371)

Configurations/10-main.conf

@@ -706,6 +706,7 @@ my %targets = (
         inherit_from     => [ "linux-generic32" ],
         asm_arch         => 'ppc32',
         perlasm_scheme   => "linux32",
+        lib_cppflags     => add("-DB_ENDIAN"),
     },
     "linux-ppc64" => {
         inherit_from     => [ "linux-generic64" ],