fix have_compiler when cross-compiling

the short cut introduced by the commit 5e55318 must depend on `$Config{'usecrosscompile'}`.

Author: fperrad

t/lib/MakeMaker/Test/Utils.pm

@@ -359,7 +359,7 @@ Returns true if there is a compiler available for XS builds.
 =cut
 
 sub have_compiler {
-    return 1 if $ENV{PERL_CORE};
+    return $Config{'usecrosscompile'} ? 0 : 1 if $ENV{PERL_CORE};
 
     my $have_compiler = 0;