Allow disabled dependencies when SOONG_ALLOW_MISSING_DEPENDENCIES is set

Push the "depens on a disabled module" dependency to runtime when
SOONG_ALLOW_MISSING_DEPENDENCIES is set so that subsets of the tree
can build when some modules are disabled.

Test: external/clang/build.py on llvm branch
Change-Id: I47e4f41d04aa3df173757f03a0c581b0bafb93f0

cc/cc.go

@@ -834,7 +834,11 @@ func (c *Module) depsToPaths(ctx android.ModuleContext) PathDeps {
 		}
 
 		if !a.Enabled() {
-			ctx.ModuleErrorf("depends on disabled module %q", name)
+			if ctx.AConfig().AllowMissingDependencies() {
+				ctx.AddMissingDependencies([]string{name})
+			} else {
+				ctx.ModuleErrorf("depends on disabled module %q", name)
+			}
 			return
 		}