Add support for workspace root packages

Author: Christian Weichel

BUILD

@@ -0,0 +1,9 @@
+packages:
+- name: app
+  type: go
+  srcs:
+  - "**/*.go"
+  - go.mod
+  - go.sum
+  config:
+    library: false

WORKSPACE

@@ -0,0 +1 @@
+defaultTarget: ":app"

pkg/leeway/build.go

@@ -294,6 +294,8 @@ func (p *Package) build(buildctx *buildContext) (err error) {
 	pkgdir = strings.Replace(pkgdir, "/", "-", -1)
 	pkgdir = strings.Replace(pkgdir, ":", "--", -1)
 	pkgdir = pkgdir + "." + version
+	// components in the workspace root would otherwise start with -- which breaks a lot of shell commands
+	pkgdir = strings.TrimPrefix(pkgdir, "--")
 
 	builddir := filepath.Join(buildctx.BuildDir(), pkgdir)
 	if _, err := os.Stat(builddir); !os.IsNotExist(err) {