Hide more warnings when building slycot.

Change-Id: I7eca8596dc2cf82fcba04e5b53b6559f70c50279
diff --git a/tools/build_rules/fortran.bzl b/tools/build_rules/fortran.bzl
index c67884a..ff940af 100644
--- a/tools/build_rules/fortran.bzl
+++ b/tools/build_rules/fortran.bzl
@@ -18,6 +18,7 @@
                    '-Werror',
                    '-Wextra',
                    '-Wno-builtin-macro-redefined',
+                   '-Wunused-local-typedefs',
                    '-D__has_feature(x)=0',
                    '-fmacro-backtrace-limit=0']