Revert "Don't preopt on eng builds."

This reverts commit 7effde0048bcce6084e00bf29ff3bea4f34d1599.

Bug: 25801231
Bug: 26794212
diff --git a/core/dex_preopt.mk b/core/dex_preopt.mk
index de0b80a..6499b63 100644
--- a/core/dex_preopt.mk
+++ b/core/dex_preopt.mk
@@ -21,13 +21,9 @@
 
 # The default values for pre-opting: always preopt PIC.
 # Conditional to building on linux, as dex2oat currently does not work on darwin.
-# Conditional to building a non-eng build, as it currently negatively affects
-# some development workflows.
-ifneq ($(TARGET_BUILD_VARIANT),eng)
-  ifeq ($(HOST_OS),linux)
-    WITH_DEXPREOPT_PIC ?= true
-    WITH_DEXPREOPT ?= true
-  endif
+ifeq ($(HOST_OS),linux)
+  WITH_DEXPREOPT_PIC ?= true
+  WITH_DEXPREOPT ?= true
 endif
 
 # $(1): the .jar or .apk to remove classes.dex