Fix setting -shims flag in interop plugin (#2729)

buildSrc/plugins/src/main/groovy/org/jetbrains/kotlin/NativeInteropPlugin.groovy

@@ -254,8 +254,8 @@ class NamedNativeInteropConfig implements Named {
                     args '-header', it
                 }
 
-                if (project.hasProperty('shims')) {
-                    args '-shims', project.ext.shims
+                if (project.hasProperty('shims') && project.ext.shims) {
+                    args '-shims'
                 }
 
             }

tools/kotlin-native-gradle-plugin/src/test/groovy/org/jetbrains/kotlin/gradle/plugin/test/IncrementalSpecification.groovy

@@ -208,7 +208,7 @@ class IncrementalSpecification extends BaseKonanSpecification {
         "linkerOpts"             | "'--help'"
         "includeDirs"            | "'src'"
         "includeDirs.allHeaders" | "'src'"
-        "extraOpts"              | "'-shims', 'false'"
+        "extraOpts"              | "'-shims'"
         "noDefaultLibs"          | "true"
     }