src/runtime: add runtime.Version()

This adds the `Version()` function of the `runtime` package which embeds
the go version that was used to build tinygo.

For programs that are compiled with tinygo the version can be overriden
via the:
`tinygo build -ldflags="-X 'runtime.buildVersion=abc'"` flag.
Otherwise it will continue to use the go version with which tinygo was
compiled.

Author: ZauberNerd

builder/build.go

@@ -195,6 +195,12 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 	var packageJobs []*compileJob
 	packageBitcodePaths := make(map[string]string)
 	packageActionIDs := make(map[string]string)
+
+	if config.Options.GlobalValues["runtime"]["buildVersion"] == "" {
+		version, _ := goenv.GorootVersionString(goenv.Get("GOROOT"))
+		config.Options.GlobalValues["runtime"] = map[string]string{"buildVersion": version}
+	}
+
 	for _, pkg := range lprogram.Sorted() {
 		pkg := pkg // necessary to avoid a race condition
 

src/runtime/extern.go

@@ -3,3 +3,17 @@ package runtime
 func Callers(skip int, pc []uintptr) int {
 	return 0
 }
+
+// buildVersion is the Go tree's version string at build time.
+//
+// This is set by the linker.
+//
+// This is accessed by "go version <binary>".
+var buildVersion string
+
+// Version returns the Go tree's version string.
+// It is either the commit hash and date at the time of the build or,
+// when possible, a release tag like "go1.3".
+func Version() string {
+	return buildVersion
+}