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hexen: Fix desync of demo1 on some platforms/compilers

Official release of Hexen's source code relies on unspecified behavior the in order of function's argument evaluation, see ISO-IEC 9899-1999, [6.5.2.2.10]
P_Random() are called in different parameters of P_SpawnMobj() within A_LeafSpawn()

--- a/src/hexen/a_action.c

+++ b/src/hexen/a_action.c

@@ -295,10 +295,15 @@

     for (i = (P_Random() & 3) + 1; i; i--)

     {

-        mo = P_SpawnMobj(actor->x + ((P_Random() - P_Random()) << 14),

-                         actor->y + ((P_Random() - P_Random()) << 14),

-                         actor->z + (P_Random() << 14),

-                         MT_LEAF1 + (P_Random() & 1));

+        // Official release of Hexen's source code relies on unspecified behavior

+        // the in order of function's argument evaluation,

+        // see ISO-IEC 9899-1999, [6.5.2.2.10]

+        mobjtype_t type = MT_LEAF1 + (P_Random() & 1);

+        fixed_t z = actor->z + (P_Random() << 14);

+        fixed_t y = actor->y + ((P_Random() - P_Random()) << 14);

+        fixed_t x = actor->x + ((P_Random() - P_Random()) << 14);

+

+        mo = P_SpawnMobj(x, y, z, type);

         if (mo)

         {

             P_ThrustMobj(mo, actor->angle, (P_Random() << 9) + 3 * FRACUNIT);