cgo: run CGo parser for all CGo fragments in a file

Previously, libclang was run on each fragment (import "C") separately.
However, in regular Go it's possible for later fragments to refer to
types in earlier fragments so they must have been parsed as one.

This commit changes the behavior to run only one C parser invocation for
each Go file.

builder/build.go

@@ -21,6 +21,7 @@ import (
 	"sort"
 	"strings"
 
+	"github.com/tinygo-org/tinygo/cgo"
 	"github.com/tinygo-org/tinygo/compileopts"
 	"github.com/tinygo-org/tinygo/compiler"
 	"github.com/tinygo-org/tinygo/goenv"
@@ -60,6 +61,7 @@ type BuildResult struct {
 // implementation of an imported package changes.
 type packageAction struct {
 	ImportPath       string
+	CGoVersion       int // cgo.Version
 	CompilerVersion  int // compiler.Version
 	InterpVersion    int // interp.Version
 	LLVMVersion      string
@@ -179,6 +181,7 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 		// the parameters for the build.
 		actionID := packageAction{
 			ImportPath:       pkg.ImportPath,
+			CGoVersion:       cgo.Version,
 			CompilerVersion:  compiler.Version,
 			InterpVersion:    interp.Version,
 			LLVMVersion:      llvm.Version,