[K/N][build] Use -Werror when compiling C or C++ in NativeInteropPlugin

Now that this compilation doesn't emit any warnings, this commit adds
`-Werror` to it to prevent new warnings.

Author: SvyatoslavScherbina

kotlin-native/build-tools/src/main/kotlin/org/jetbrains/kotlin/interop/NativeInteropPlugin.kt

@@ -263,14 +263,15 @@ open class NativeInteropPlugin : Plugin<Project> {
                     val cflags = cCompilerArgs +
                             commonCompilerArgs +
                             ignoreWarningFlags +
+                            "-Werror" +
                             includeDirs.map { "-I${it.absolutePath}" } +
                             hostPlatform.clangForJni.hostCompilerArgsForJni
 
                     flags(*cflags.toTypedArray(), "-c", "-o", ruleOut(), ruleInFirst())
                 }
                 (".cpp" to ".$obj") {
                     tool(*hostPlatform.clang.clangCXX("").toTypedArray())
-                    val cxxflags = cppCompilerArgs + commonCompilerArgs + includeDirs.map { "-I${it.absolutePath}" }
+                    val cxxflags = cppCompilerArgs + commonCompilerArgs + "-Werror" + includeDirs.map { "-I${it.absolutePath}" }
                     flags(*cxxflags.toTypedArray(), "-c", "-o", ruleOut(), ruleInFirst())
                 }
             }