Resolve #1168 by way of a makeshift, in absence of better isolation of the ksp environment.

Author: cgruber

src/main/kotlin/io/bazel/kotlin/builder/toolchain/KotlinToolchain.kt

@@ -20,6 +20,7 @@ import io.bazel.kotlin.builder.utils.BazelRunFiles
 import io.bazel.kotlin.builder.utils.resolveVerified
 import io.bazel.kotlin.builder.utils.verified
 import io.bazel.kotlin.builder.utils.verifiedPath
+import org.jetbrains.kotlin.preloading.ClassCondition
 import org.jetbrains.kotlin.preloading.ClassPreloadingUtils
 import org.jetbrains.kotlin.preloading.Preloader
 import java.io.File
@@ -233,9 +234,11 @@ class KotlinToolchain private constructor(
           }
         },
         Preloader.DEFAULT_CLASS_NUMBER_ESTIMATE,
-        classLoader,
-        null,
-      )
+        classLoader
+      ) { className ->
+        // Preload guava to avoid weird isolation issues.
+        className.startsWith("com.google.common.")
+      }
     }.onFailure {
       throw RuntimeException("$javaHome, $baseJars", it)
     }.getOrThrow()