aarch64: Move return value handling into ffi_call_SYSV

This lets us pass return data directly to the caller of ffi_call
in most cases, rather than storing it into temporary storage first.

src/aarch64/internal.h

@@ -18,7 +18,48 @@ CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
 
-#define AARCH64_FLAG_ARG_V_BIT	0
+#define AARCH64_RET_VOID	0
+#define AARCH64_RET_INT64	1
+#define AARCH64_RET_INT128	2
+
+#define AARCH64_RET_UNUSED3	3
+#define AARCH64_RET_UNUSED4	4
+#define AARCH64_RET_UNUSED5	5
+#define AARCH64_RET_UNUSED6	6
+#define AARCH64_RET_UNUSED7	7
+
+/* Note that FFI_TYPE_FLOAT == 2, _DOUBLE == 3, _LONGDOUBLE == 4,
+   so _S4 through _Q1 are layed out as (TYPE * 4) + (4 - COUNT).  */
+#define AARCH64_RET_S4		8
+#define AARCH64_RET_S3		9
+#define AARCH64_RET_S2		10
+#define AARCH64_RET_S1		11
+
+#define AARCH64_RET_D4		12
+#define AARCH64_RET_D3		13
+#define AARCH64_RET_D2		14
+#define AARCH64_RET_D1		15
+
+#define AARCH64_RET_Q4		16
+#define AARCH64_RET_Q3		17
+#define AARCH64_RET_Q2		18
+#define AARCH64_RET_Q1		19
+
+/* Note that each of the sub-64-bit integers gets two entries.  */
+#define AARCH64_RET_UINT8	20
+#define AARCH64_RET_UINT16	22
+#define AARCH64_RET_UINT32	24
+
+#define AARCH64_RET_SINT8	26
+#define AARCH64_RET_SINT16	28
+#define AARCH64_RET_SINT32	30
+
+#define AARCH64_RET_MASK	31
+
+#define AARCH64_RET_IN_MEM	(1 << 5)
+#define AARCH64_RET_NEED_COPY	(1 << 6)
+
+#define AARCH64_FLAG_ARG_V_BIT	7
 #define AARCH64_FLAG_ARG_V	(1 << AARCH64_FLAG_ARG_V_BIT)
 
 #define N_X_ARG_REG		8