alpha: Reorganize cif flags

Unties the backend from changes to FFI_TYPE_* constants, and allows
compilation to succeed after the addition of FFI_TYPE_COMPLEX.

Delete the hand-written unwind info.

src/alpha/internal.h

@@ -0,0 +1,19 @@
+#define ALPHA_ST_VOID	0
+#define ALPHA_ST_INT	1
+#define ALPHA_ST_FLOAT	2
+#define ALPHA_ST_DOUBLE	3
+
+#define ALPHA_LD_VOID	0
+#define ALPHA_LD_INT64	1
+#define ALPHA_LD_INT32	2
+#define ALPHA_LD_UINT16	3
+#define ALPHA_LD_SINT16	4
+#define ALPHA_LD_UINT8	5
+#define ALPHA_LD_SINT8	6
+#define ALPHA_LD_FLOAT	7
+#define ALPHA_LD_DOUBLE	8
+
+#define ALPHA_ST_SHIFT		0
+#define ALPHA_LD_SHIFT		8
+#define ALPHA_RET_IN_MEM	0x10000
+#define ALPHA_FLAGS(S, L)	(((L) << ALPHA_LD_SHIFT) | (S))