Make Throwable.addSuppressed extension work without kotlin-stdlib-jdk7*

*given that it runs on JDK7 and higher. The addSuppressed member
is called with reflection when it's available.
kotlin-stdlib-jdk7 extension still overrides that and calls
addSuppressed member statically as before.

#KT-30560 Fixed

libraries/stdlib/jdk7/build.gradle

@@ -12,11 +12,6 @@ pill {
     importAsLibrary = true
 }
 
-dependencies {
-    compile project(':kotlin-stdlib')
-    testCompile project(':kotlin-test:kotlin-test-junit')
-}
-
 sourceSets {
     main {
         kotlin {
@@ -33,6 +28,11 @@ sourceSets {
             }
         }
     }
+    noJdk7Test {
+        kotlin {
+            srcDir 'testNoJdk7'
+        }
+    }
     java9 {
         java {
             srcDir 'java9'
@@ -40,6 +40,15 @@ sourceSets {
     }
 }
 
+configurations {
+    noJdk7TestCompile.extendsFrom(testCompile)
+}
+
+dependencies {
+    compile project(':kotlin-stdlib')
+    testCompile project(':kotlin-test:kotlin-test-junit')
+}
+
 jar {
     manifestAttributes(manifest, project, 'Main' /*true*/)
     // TODO: enable as soon as this doesn't cause D8/DX to crash
@@ -106,4 +115,15 @@ task testJdk6Tests(type: Test) {
     }
 }
 
-check.dependsOn testJdk6Tests
+task testNoJdk7(type: Test, dependsOn: noJdk7TestClasses) {
+    group = "verification"
+
+    executable = "$JDK_17/bin/java"
+
+    testClassesDirs = sourceSets.noJdk7Test.output.classesDirs
+    classpath = sourceSets.noJdk7Test.runtimeClasspath
+}
+
+
+check.dependsOn testJdk6Tests, testNoJdk7
+