Works around the -fPIC issue for rust

Rust binaries are compiled with -fPIC by default, and this fights with
bazel's default of -fno-pic when using `-c opt` mode.  This has caused
the compilation to fail.

After some running around with hair on fire, I found
bazelbuild/rules_rust#118, which seems to
work around the issue.

I think in the long run, rules_rust should handle this automagically for
the users.

Author: filmil

kythe/rust/fuchsia_extractor/BUILD

@@ -25,6 +25,13 @@ rust_test(
       "//kythe/rust/cargo:tempdir",
     ],
     edition = "2018",
+    # See https://github.com/bazelbuild/rules_rust/issues/118.  Without this,
+    # rust binaries require their deps to be compiled with -fPIC, which is not
+    # always the case. fastbuild and dbg use -fPIC, but opt does not; and rust
+    # build rules are not yet sophisticated enough to know the difference.
+    rustc_flags = [
+        "-Crelocation-model=static",
+    ],
 )
 
 rust_clippy(