all: refactor compile options

Move most of the logic of determining which compiler configuration to
use (such as GOOS/GOARCH, build tags, whether to include debug symbols,
panic strategy, etc.) into the compileopts package. This makes it a
single source of truth for anything related to compiler configuration.

It has a few advantages:

  * The compile configuration is independent of the compiler package.
    This makes it possible to move optimization passes out of the
    compiler, as they don't rely on compiler.Config anymore.
  * There is only one place to look if an incorrect compile option is
    used.
  * The compileopts provides some resistance against unintentionally
    picking the wrong option, such as with c.selectGC() vs c.GC() in the
    compiler.
  * It is now a lot easier to change compile options, as most options
    are getters now.

compiler/optimizer.go

@@ -19,12 +19,12 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) erro
 	}
 	builder.AddCoroutinePassesToExtensionPoints()
 
-	if c.PanicStrategy == "trap" {
+	if c.PanicStrategy() == "trap" {
 		c.replacePanicsWithTrap() // -panic=trap
 	}
 
 	// run a check of all of our code
-	if c.VerifyIR {
+	if c.VerifyIR() {
 		err := c.checkModule()
 		if err != nil {
 			return err
@@ -96,7 +96,7 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) erro
 			return err
 		}
 	}
-	if c.VerifyIR {
+	if c.VerifyIR() {
 		if err := c.checkModule(); err != nil {
 			return err
 		}