Add warning if unable to preprocess a file

Author: facchinm

Diff for: constants/constants.go

@@ -161,6 +161,7 @@ const MSG_BOOTLOADER_FILE_MISSING = "Bootloader file specified but missing: {0}"
 const MSG_BUILD_OPTIONS_CHANGED = "Build options changed, rebuilding all"
 const MSG_CANT_FIND_SKETCH_IN_PATH = "Unable to find {0} in {1}"
 const MSG_FQBN_INVALID = "{0} is not a valid fully qualified board name. Required format is targetPackageName:targetPlatformName:targetBoardName."
+const MSG_FIND_INCLUDES_FAILED = "Failed to find includes in file {1}"
 const MSG_INVALID_QUOTING = "Invalid quoting: no closing [{0}] char found."
 const MSG_IGNORED_BUILTIN_TOOLS_TXT = "Skipping {0}; please consider removing that file since it may hurt older Arduino installations"
 const MSG_LIB_LEGACY = "(legacy)"

Diff for: container_find_includes.go

@@ -343,6 +343,9 @@ func findIncludesUntilDone(ctx *types.Context, cache *includeCache, sourceFile t
 				return i18n.WrapError(preproc_err)
 			} else {
 				include = IncludesFinderWithRegExp(ctx, string(preproc_stderr))
+				if include == "" {
+					ctx.GetLogger().Println(constants.LOG_LEVEL_DEBUG, constants.MSG_FIND_INCLUDES_FAILED, sourcePath)
+				}
 			}
 		}