[SOL] sbfv2: output _RELATIVE relocations in a separate SHT_RELR section

sbfv2 only produces _RELATIVE relocations and those can be packed much more
efficiently using SHT_RELR. See https://reviews.llvm.org/D48247.

Author: alessandrod

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -346,6 +346,7 @@ impl<'a> GccLinker<'a> {
                 if self.sess.opts.cg.target_cpu.as_ref().unwrap_or(&self.sess.target.cpu) == "sbfv2"
                 {
                     self.linker_arg("--section-start=.text=0x100000000");
+                    self.linker_arg("--pack-dyn-relocs=relr");
                 }
             }
         }