Test basic DWARF generation (#931)

* Add obj generation with debug info
* Add simple transform check

.github/actions/define-dwarfdump-env/README.md

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+# define-dwarfdump-env
+
+Defines `DWARFDUMP` path executable.

.github/actions/define-dwarfdump-env/action.yml

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+name: 'Set up a DWARFDUMP env'
+description: 'Set up a DWARFDUMP env (see tests/debug/dump.rs)'
+
+runs:
+  using: node12
+  main: 'main.js'

.github/actions/define-dwarfdump-env/main.js

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+#!/usr/bin/env node
+
+// On OSX pointing to brew's LLVM location.
+if (process.platform == 'darwin') {
+  console.log("::set-env name=DWARFDUMP::/usr/local/opt/llvm/bin/llvm-dwarfdump");
+}
+
+// On Linux pointing to specific version
+if (process.platform == 'linux') {
+  console.log("::set-env name=DWARFDUMP::/usr/bin/llvm-dwarfdump-9");
+}