[solidity,llvm-context] Improve support for debugging the compiler (#32)

Add option --recursive-process-input <filename> for use with
--recursive-process to specify the name of a file to use instead of
reading from stdin.

If --debug-output-dir is set, dump the file passed to the recursive
invocation of the compiler as a JSON file suitable for use with
--recursive-process-input.

These changes are intended to support debugging the compiler and are
only available with DEBUG builds.

crates/solidity/src/resolc/main.rs

@@ -47,7 +47,13 @@ fn main_inner() -> anyhow::Result<()> {
     revive_llvm_context::initialize_target(revive_llvm_context::Target::PVM); // TODO: pass from CLI
 
     if arguments.recursive_process {
-        return revive_solidity::run_process();
+        #[cfg(debug_assertions)]
+        if let Some(fname) = arguments.recursive_process_input {
+            let mut infile = std::fs::File::open(fname)?;
+            return revive_solidity::run_process(Some(&mut infile));
+        }
+
+        return revive_solidity::run_process(None);
     }
 
     let debug_config = match arguments.debug_output_directory {