Fix proc-macro dynamic lib

.gitignore

@@ -1,2 +1,3 @@
 Cargo.lock
 target
+cobertura.xml

Makefile

@@ -0,0 +1,10 @@
+# These hacks are required for the test binaries depending on the dynamic library libstd-*.so
+# See: https://github.com/rust-lang/cargo/issues/4651
+#
+# We also need to exclude the derive macro from coverage because it will always show as 0% by
+# virtue of executing at compile-time outside the view of Tarpaulin.
+coverage:
+	env LD_LIBRARY_PATH="$(shell rustc --print sysroot)/lib" \
+	cargo-tarpaulin --workspace --all-features --out xml --exclude tree_hash_derive
+
+.PHONY: coverage