Specify common sources for stdlib test compilation tasks

Some multiplatform tests are compiled in single-platform projects:
- in kotlin-stdlib-jdk7
- in kotlin-stdlib-jdk8
- in kotlin-stdlib-js-ir. The latter is technically MPP but with a
single platform, so its common sources are not considered as common.

Pass information about common sources to test compilation tasks in order
to use OptionalExpectation annotations there.

Co-authored-by: Svyatoslav Scherbina <svyatoslav.scherbina@jetbrains.com>

libraries/stdlib/jdk7/build.gradle

@@ -90,6 +90,7 @@ compileTestKotlin {
             "-Xopt-in=kotlin.ExperimentalUnsignedTypes",
             "-Xopt-in=kotlin.ExperimentalStdlibApi",
             "-Xopt-in=kotlin.io.path.ExperimentalPathApi",
+            "-Xcommon-sources=${fileTree('../test').join(',')}",
     ]
 }