[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/arguments.rs

@@ -164,6 +164,12 @@ pub struct Arguments {
     /// Only for usage from within the compiler.
     #[structopt(long = "recursive-process")]
     pub recursive_process: bool,
+
+    /// Specify the input file to use instead of stdin when --recursive-process is given.
+    /// This is only intended for use when developing the compiler.
+    #[cfg(debug_assertions)]
+    #[structopt(long = "recursive-process-input")]
+    pub recursive_process_input: Option<String>,
 }
 
 impl Default for Arguments {
@@ -185,6 +191,20 @@ impl Arguments {
             anyhow::bail!("No other options are allowed while getting the compiler version.");
         }
 
+        #[cfg(debug_assertions)]
+        if self.recursive_process_input != None && !self.recursive_process {
+            anyhow::bail!("--process-input can be only used when --recursive-process is given");
+        }
+
+        #[cfg(debug_assertions)]
+        if self.recursive_process
+            && ((self.recursive_process_input == None && std::env::args().count() > 2)
+                || (self.recursive_process_input != None && std::env::args().count() > 4))
+        {
+            anyhow::bail!("No other options are allowed in recursive mode.");
+        }
+
+        #[cfg(not(debug_assertions))]
         if self.recursive_process && std::env::args().count() > 2 {
             anyhow::bail!("No other options are allowed in recursive mode.");
         }