fix set gp on riscv

src/arch/riscv/initcode.S

@@ -3,6 +3,13 @@
 .text
 .globl _start
 _start:
+    # set gp
+.option push
+.option norelax
+1:  auipc gp, %pcrel_hi(__global_pointer$)
+    addi  gp, gp, %pcrel_lo(1b)
+.option pop
+
     # call user-program function
     LOAD a0, 0(sp)
     addi a1, sp, (__riscv_xlen / 8)