Fix riscv64 trampoline to be compatible with PIC (#141)

Author: andreas-schwab

src/trampolines/trampolines_riscv64.S

@@ -9,8 +9,8 @@
 .p2align    2 SEP \
  MANGLE(UNDERSCORE(name))##: SEP \
     li t4, SYMBOL_IDX(idx) SEP \
-    auipc t3, %pcrel_hi(NAMEADDR(name)) SEP \
-    ld t3, %pcrel_lo(MANGLE(UNDERSCORE(name)))(t3) SEP \
+    la t3, NAMEADDR(name) SEP \
+    ld t3, 0(t3) SEP \
     jr t3 SEP \
 .cfi_endproc SEP \