Workaround in FloatMathTest.powers to avoid failures with js-ir runtime

Include kotlin-stdlib-js-ir in local core libs build/test and
enable failing build on test failures.

Relates to: KT-24975

build.gradle.kts

@@ -251,9 +251,7 @@ val coreLibProjects = listOfNotNull(
     ":kotlin-stdlib",
     ":kotlin-stdlib-common",
     ":kotlin-stdlib-js",
-    // Local builds are disabled at the request of the lib team
-    // TODO: Enable when tests are fixed
-    ":kotlin-stdlib-js-ir".takeIf { isTeamcityBuild },
+    ":kotlin-stdlib-js-ir",
     ":kotlin-stdlib-jdk7",
     ":kotlin-stdlib-jdk8",
     ":kotlin-test:kotlin-test-common",