T3736 fails with an unreg compiler due to printing a warning about conflicting types for memcpy:

$ ghc -dno-debug-output  -v0 -O --make T3736 -rtsopts -keep-tmp-files
/tmp/ghc4352_0/ghc4352_0.hc: In function ‘s2E3_ret’:

/tmp/ghc4352_0/ghc4352_0.hc:1494:0:
     warning: conflicting types for built-in function ‘memcpy’

Line 1494 is

;EF_(memcpy);

in:

if ((W_)((W_)Hp > (W_)HpLim)) goto _c2MC;
_s2yO = (Sp[4]) + 0x10UL;
_s2Ed = Sp[2];
_s2yS = (*((P_)(R1.w+7))) * 0x4UL;
_s2Ee = (Sp[5]) + _s2yS;
;EF_(memcpy);
{void * (*ghcFunPtr)(void *, void *, W_);
ghcFunPtr = ((void * (*)(void *, void *, W_))(W_)&memcpy);
_s2Eg = (W_)ghcFunPtr((void *)_s2yO, (void *)_s2Ee, _s2Ed);;}
Hp[-12] = (W_)&base_GHCziSTRef_STRef_con_info;
Hp[-11] = Sp[1];
Hp[-10] = (W_)&base_GHCziForeignPtr_MallocPtr_con_info;
Hp[-9] = Sp[4];
Hp[-8] = (W_)Hp-95;