x86-64: {,V}CVT{,U}SI2Sx are ambiguous without suffix

x86-64: {,V}CVT{,U}SI2Sx are ambiguous without suffix

For 64-bit these should not be emitted without suffix in AT&T mode (as
being ambiguous that way); the suffixes are benign for 32-bit. For
consistency also omit the suffix in Intel mode for {,V}CVTSI2SxQ.

The omission has originally (prior to rev 260691) lead to wrong code
being generated for the 64-bit unsigned-to-float/double conversions (as
gas guesses an L suffix instead of the required Q one when the operand
is in memory). In all remaining cases (being changed here) the omission
would "just" lead to warnings with future gas versions.

As a result, arrange to check for the L suffixes in 32-bit test cases.

In order for related test cases to actually test what they're supposed
to test, add (seemingly unrelated) a few empty "asm volatile()".
Presumably there are more where constant propagation voids the intended
effect of the tests, but these are ones helping make sure the assembler
actually still assembles correctly the output after the changes here.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@267833 138bc75d-0d04-0410-961f-82ee72b054a4