Suport passing arbitrary llvm arguments (#271)

- Support for passing LLVM command line options via the prcoess input or
providing one or more `--llvm-arg='..'` resolc CLI flag. This allows
more fine-grained control over the LLVM backend configuration.
- Make LLVM initialization idempotent.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/solidity/src/project/mod.rs

@@ -66,6 +66,7 @@ impl Project {
         optimizer_settings: revive_llvm_context::OptimizerSettings,
         include_metadata_hash: bool,
         debug_config: revive_llvm_context::DebugConfig,
+        llvm_arguments: &[String],
     ) -> anyhow::Result<Build> {
         let project = self.clone();
         #[cfg(feature = "parallel")]
@@ -81,6 +82,7 @@ impl Project {
                     include_metadata_hash,
                     optimizer_settings.clone(),
                     debug_config.clone(),
+                    llvm_arguments.to_vec(),
                 );
                 let process_output = {
                     #[cfg(target_os = "emscripten")]
@@ -316,6 +318,7 @@ impl revive_llvm_context::PolkaVMDependency for Project {
         optimizer_settings: revive_llvm_context::OptimizerSettings,
         include_metadata_hash: bool,
         debug_config: revive_llvm_context::DebugConfig,
+        llvm_arguments: &[String],
     ) -> anyhow::Result<String> {
         let contract_path = project.resolve_path(identifier)?;
         let contract = project
@@ -335,6 +338,7 @@ impl revive_llvm_context::PolkaVMDependency for Project {
                 optimizer_settings,
                 include_metadata_hash,
                 debug_config,
+                llvm_arguments,
             )
             .map_err(|error| {
                 anyhow::anyhow!(