add rv64 backend

It is mostly complete, but still has a few ABI bugs when passing
floats in structs, or when structs are passed partly in register,
and partly on stack.

rv64/targ.c

@@ -0,0 +1,53 @@
+#include "all.h"
+
+Rv64Op rv64_op[NOp] = {
+#define O(op, t, x) [O##op] =
+#define V(imm) { imm },
+#include "../ops.h"
+};
+
+int rv64_rsave[] = {
+	T0, T1, T2, T3, T4, T5,
+	A0, A1, A2, A3, A4, A5, A6, A7,
+	FA0, FA1, FA2,  FA3,  FA4, FA5, FA6, FA7,
+	FT0, FT1, FT2,  FT3,  FT4, FT5, FT6, FT7,
+	FT8, FT9, FT10, FT11,
+	-1
+};
+int rv64_rclob[] = {
+	     S1,  S2,   S3,   S4,  S5,  S6,  S7,
+	S8,  S9,  S10,  S11,
+	FS0, FS1, FS2,  FS3,  FS4, FS5, FS6, FS7,
+	FS8, FS9, FS10, FS11,
+	-1
+};
+
+/* T6 used as swap register (TODO: is there a better choice?) */
+#define RGLOB (BIT(FP) | BIT(SP) | BIT(GP) | BIT(TP) | BIT(RA) | BIT(T6))
+
+static int
+rv64_memargs(int op)
+{
+	(void)op;
+	return 0;
+}
+
+Target T_rv64 = {
+	.gpr0 = T0,
+	.ngpr = NGPR,
+	.fpr0 = FT0,
+	.nfpr = NFPR,
+	.rglob = RGLOB,
+	.nrglob = 6,
+	.rsave = rv64_rsave,
+	.nrsave = {NGPS, NFPS},
+	.retregs = rv64_retregs,
+	.argregs = rv64_argregs,
+	.memargs = rv64_memargs,
+	.abi = rv64_abi,
+	.isel = rv64_isel,
+	.emitfn = rv64_emitfn,
+};
+
+MAKESURE(rsave_size_ok, sizeof rv64_rsave == (NGPS+NFPS+1) * sizeof(int));
+MAKESURE(rclob_size_ok, sizeof rv64_rclob == (NCLR+1) * sizeof(int));