Update flags passed to kotlinc

- Remove -Xuse-ir as it is default in Kotlin 1.5
- Add -Xsam-conversions=class for KT-46512

Change-Id: Ie351bb9ad5ec51ef7b7346d0076868d04cfe9811
diff --git a/java/base.go b/java/base.go
index 03652be..ef8c563 100644
--- a/java/base.go
+++ b/java/base.go
@@ -895,8 +895,8 @@
 		kotlincFlags := j.properties.Kotlincflags
 		CheckKotlincFlags(ctx, kotlincFlags)
 
-		// Dogfood the JVM_IR backend.
-		kotlincFlags = append(kotlincFlags, "-Xuse-ir")
+		// Workaround for KT-46512
+		kotlincFlags = append(kotlincFlags, "-Xsam-conversions=class")
 
 		// If there are kotlin files, compile them first but pass all the kotlin and java files
 		// kotlinc will use the java files to resolve types referenced by the kotlin files, but