cpu.x86.64: fix calling varargs functions

basis/cpu/x86/32/32.factor

@@ -209,6 +209,8 @@ M:: x86.32 %binary-float-function ( dst src1 src2 func -- )
     #! MINGW ABI incompatibility disaster
     [ large-struct? ] [ mingw eq? os windows? not or ] bi* and ;
 
+M: x86.32 %prepare-var-args ( -- ) ;
+
 M:: x86.32 stack-cleanup ( stack-size return abi -- n )
     #! a) Functions which are stdcall/fastcall/thiscall have to
     #! clean up the caller's stack frame.

basis/cpu/x86/64/64.factor

@@ -140,6 +140,8 @@ M:: x86.64 %binary-float-function ( dst src1 src2 func -- )
     func "libm" load-library f %c-invoke
     dst double-rep %load-return ;
 
+M: x86.64 %prepare-var-args ( -- ) RAX RAX XOR ;
+
 M: x86.64 stack-cleanup 3drop 0 ;
 
 M: x86.64 %cleanup 0 assert= ;

basis/cpu/x86/x86.factor

@@ -347,8 +347,8 @@ M: x86.64 has-small-reg? 2drop t ;
 
 :: (%convert-integer) ( dst src bits quot -- )
     dst { src } bits [| new-dst |
-        new-dst dup bits n-bit-version-of dup src MOV
-        quot call
+        new-dst src int-rep %copy
+        new-dst dup bits n-bit-version-of quot call
         dst new-dst int-rep %copy
     ] with-small-register ; inline
 
@@ -644,6 +644,7 @@ HOOK: %cleanup cpu ( n -- )
 :: emit-alien-insn ( reg-inputs stack-inputs reg-outputs cleanup stack-size quot -- )
     stack-inputs [ first3 %store-stack-param ] each
     reg-inputs [ first3 %store-reg-param ] each
+    %prepare-var-args
     quot call
     cleanup %cleanup
     reg-outputs [ first3 %load-reg-param ] each ; inline