Fix linkage for large binaries on mips64 platforms ...

... by enabling xgot feature

Co-Authored-By: Zixing Liu <zixing.liu@canonical.com>

src/bootstrap/bootstrap.py

@@ -877,6 +877,12 @@ class RustBuild(object):
 
         # preserve existing RUSTFLAGS
         env.setdefault("RUSTFLAGS", "")
+        # we need to explicitly add +xgot here so that we can successfully bootstrap
+        # a usable stage1 compiler
+        # FIXME: remove this if condition on the next bootstrap bump
+        # cfg(bootstrap)
+        if self.build_triple().startswith('mips'):
+            env["RUSTFLAGS"] += " -Ctarget-feature=+xgot"
         target_features = []
         if self.get_toml("crt-static", build_section) == "true":
             target_features += ["+crt-static"]