compiler: move settings to a separate Config struct

Moving settings to a separate config struct has two benefits:
  - It decouples the compiler a bit from other packages, most
    importantly the compileopts package. Decoupling is generally a good
    thing.
  - Perhaps more importantly, it precisely specifies which settings are
    used while compiling and affect the resulting LLVM module. This will
    be necessary for caching the LLVM module.
    While it would have been possible to cache without this refactor, it
    would have been very easy to miss a setting and thus let the
    compiler work with invalid/stale data.

builder/build.go

@@ -45,10 +45,27 @@ type BuildResult struct {
 // The error value may be of type *MultiError. Callers will likely want to check
 // for this case and print such errors individually.
 func Build(pkgName, outpath string, config *compileopts.Config, action func(BuildResult) error) error {
+	compilerConfig := &compiler.Config{
+		Triple:          config.Triple(),
+		CPU:             config.CPU(),
+		Features:        config.Features(),
+		GOOS:            config.GOOS(),
+		GOARCH:          config.GOARCH(),
+		CodeModel:       config.CodeModel(),
+		RelocationModel: config.RelocationModel(),
+
+		Scheduler:          config.Scheduler(),
+		FuncImplementation: config.FuncImplementation(),
+		AutomaticStackSize: config.AutomaticStackSize(),
+		DefaultStackSize:   config.Target.DefaultStackSize,
+		NeedsStackObjects:  config.NeedsStackObjects(),
+		Debug:              config.Debug(),
+	}
+
 	// Load the target machine, which is the LLVM object that contains all
 	// details of a target (alignment restrictions, pointer size, default
 	// address spaces, etc).
-	machine, err := compiler.NewTargetMachine(config)
+	machine, err := compiler.NewTargetMachine(compilerConfig)
 	if err != nil {
 		return err
 	}
@@ -77,7 +94,7 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 	programJob := &compileJob{
 		description: "compile Go files",
 		run: func() (err error) {
-			mod, err = compileWholeProgram(pkgName, config, lprogram, machine)
+			mod, err = compileWholeProgram(pkgName, config, compilerConfig, lprogram, machine)
 			if err != nil {
 				return
 			}
@@ -340,9 +357,9 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 
 // compileWholeProgram compiles the entire *loader.Program to a LLVM module and
 // applies most necessary optimizations and transformations.
-func compileWholeProgram(pkgName string, config *compileopts.Config, lprogram *loader.Program, machine llvm.TargetMachine) (llvm.Module, error) {
+func compileWholeProgram(pkgName string, config *compileopts.Config, compilerConfig *compiler.Config, lprogram *loader.Program, machine llvm.TargetMachine) (llvm.Module, error) {
 	// Compile AST to IR.
-	mod, errs := compiler.CompileProgram(pkgName, lprogram, machine, config)
+	mod, errs := compiler.CompileProgram(lprogram, machine, compilerConfig, config.DumpSSA())
 	if errs != nil {
 		return mod, newMultiError(errs)
 	}