add tests for void context calls to overloads

Discovered while working on another module, in many amagic_call() will
use the current context when calling the overload sub, but these APIs
might be called in XS code that simply needs a comparison, regardless
of the current OP context.

Author: tonycoz

ext/XS-APItest/APItest.xs

@@ -5035,6 +5035,14 @@ sv_numeq_flags(nullable_SV sv1, nullable_SV sv2, U32 flags)
 bool
 sv_numne(nullable_SV sv1, nullable_SV sv2)
 
+# deliberately void context
+void
+void_sv_numne(nullable_SV sv1, nullable_SV sv2, SV *out)
+    CODE:
+        sv_setbool(out, sv_numne(sv1, sv2));
+    OUTPUT:
+        out
+
 bool
 sv_numne_flags(nullable_SV sv1, nullable_SV sv2, U32 flags)
 

ext/XS-APItest/t/sv_numne.t

@@ -1,6 +1,6 @@
 #!perl
 
-use Test::More tests => 22;
+use Test::More tests => 24;
 use XS::APItest;
 use Config;
 
@@ -43,7 +43,13 @@ ok !sv_numne_flags($1, 11, SV_GMAGIC), 'sv_numne_flags with SV_GMAGIC does';
     ok !sv_numne(12, $obj), 'AlwaysTwelve is 12 on right';
     ok  sv_numne(11, $obj), 'AlwayeTwelve is not 11 on the right';
 
-    ok !sv_numne_flags($obj, 11, SV_SKIP_OVERLOAD), 'AlwaysTwelve is 12 with SV_SKIP_OVERLOAD'
+    ok !sv_numne_flags($obj, 11, SV_SKIP_OVERLOAD), 'AlwaysTwelve is 12 with SV_SKIP_OVERLOAD';
+
+    my $result;
+    void_sv_numne($obj, 11, $result);
+    ok($result, "overloaded sv_numne() (ne) in void context");
+    void_sv_numne($obj, 12, $result);
+    ok(!$result, "overloaded sv_numne() (eq) in void context");
 }
 
 # +0 overloading with large numbers and using fallback