Skip dependency detection if library is fully precompiled

Precompiled bits of a library should not depend on any link time dependency (we cannot assure ABI stability).
Fixes arduino/ArduinoCore-mbed#119

Author: facchinm

legacy/builder/container_find_includes.go

@@ -316,8 +316,18 @@ func findIncludesUntilDone(ctx *types.Context, cache *includeCache, sourceFile t
 		if library, ok := sourceFile.Origin.(*libraries.Library); ok && library.UtilityDir != nil {
 			includes = append(includes, library.UtilityDir)
 		}
+
+		if library, ok := sourceFile.Origin.(*libraries.Library); ok {
+			if library.Precompiled == true && library.PrecompiledWithSources == true {
+				// Fully precompiled libraries should have no dependencies
+				// to avoid ABI breakage
+				return nil
+			}
+		}
+
 		var preproc_err error
 		var preproc_stderr []byte
+
 		if unchanged && cache.valid {
 			include = cache.Next().Include
 			if first && ctx.Verbose {