Fix bug where bitwise binary ops on 32-bit values will be miscalculated and trash the stack in certain cases.

The following program (derived from a csmith-generated test case) demonstrates the crash:

#pragma optimize 8+64
#include <stdio.h>
long g = 0;
int main (void) {
    long l = 0x10305070;
    printf("%08lx\n", l ^ (g = (1 , 0x12345678)));
}

Gen.pas

@@ -3895,6 +3895,9 @@ procedure GenTree {op: icptr};
 	 lab1: integer;			{label number}
 
       begin {GenOp}
+      if gLong.where = A_X then
+         GenImplied(m_phx)
+      else
          GenImplied(m_pla);
       if gLong.where = constant then begin
 	 GenNative(opi, immediate, long(gLong.lval).lsw, nil, 0);