fix x86 CALLF

[ksherlock]

Reported in comp.compilers.lcc on 3/3/2013. (news:[email protected])

On compiling expression statements like

foo(); foo(); foo();

where foo is declared as

double foo(void);

the compiler generates

call foo
call foo
call foo

rather than

call foo
fstpl %st(0)
call foo
fstpl %st(0)
call foo
fstpl %st(0)

The underlying issue is that the reg: CALLF (which doesn't clean up the x87 stack) is preferred over the stmt: CALLF (which does clean up the stack). Re-ordering the stmt: CALLF first fixes the problem.