Don't wrap ProcessCanceledException with other exceptions

ProcessCanceledException indicates that the compilation process was
terminated by user. This kind of exception should not be wrapped anyhow
in order to be handled on toplevel in CLICompiler.
#KT-38483 Fixed

compiler/backend-common/src/org/jetbrains/kotlin/backend/common/CodegenUtil.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.backend.common
 
 import com.intellij.openapi.application.ApplicationManager
+import com.intellij.openapi.progress.ProcessCanceledException
 import com.intellij.openapi.project.Project
 import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.descriptors.*
@@ -236,6 +237,7 @@ object CodegenUtil {
         // CompilationException (the only KotlinExceptionWithAttachments possible here) is already supposed
         // to have all information about the context.
         if (exception is KotlinExceptionWithAttachments) throw exception
+        if (exception is ProcessCanceledException) throw exception
         throw BackendException(
             getExceptionMessage("Backend", "Exception during $phase", exception, location) +
                     additionalMessage?.let { "\n" + it }.orEmpty(),