Merge #35

35: Add .sbss section to linker script r=Disasm a=laanwj

Rust nightly has started generating this section for RISC-V executables, place it at the start of the bss area.

```
  = note: rust-lld: error: no memory region specified for section '.sbss'
```

I think this is correct, looking at other uses of the section, though I could find no definitive documentation for this.

Co-authored-by: Wladimir J. van der Laan <laanwj@gmail.com>

riscv-rt/link.x

@@ -66,7 +66,7 @@ SECTIONS
   .bss :
   {
     _sbss = .;
-    *(.bss .bss.*);
+    *(.sbss .sbss.* .bss .bss.*);
     . = ALIGN(4);
     _ebss = .;
   } > REGION_BSS :virtual