Ignore warnings for missing classpath elements with custom JAVA_HOME

Prior to this commit, the "-Werror" was removed as a command-line
argument in order not to fail the build for missing classpath elements.

This commit reinstates "-Werror" and removes "-Xlink:path" in order to
explicitly ignore warnings for missing classpath elements when executing
the build with a custom JAVA_HOME.

See gh-24474

gradle/custom-java-home.gradle

@@ -51,7 +51,9 @@ if (customJavaHome) {
 		}
 		options.fork = true
 		options.forkOptions.executable = javacExecutable
-		options.compilerArgs -= "-Werror"
+		// Ignore warnings about missing classpath elements -- for example, those picked up
+		// via Class-Path entries in MANIFEST.MF files in artifacts like xalan-2.7.2.jar.
+		options.compilerArgs -= "-Xlint:path"
 		if (customJavaSourceVersion) {
 			options.compilerArgs += [ "--release", customJavaSourceVersion]
 			inputs.property("customJavaSourceVersion", customJavaSourceVersion)