Revert "Revert "adb: support /oem partition""

This reverts commit 6084a0124f868c7ec43f6c415a27a168f27ff694.

The original build breakage is fixed by (a) building the verity
code for eng builds as well as userdebug builds and (b) moving
the exported remount service functions into a new header file.

Change-Id: Ice0c4f97d4db38ab7eb333c7a6e56bbd11123f5b
diff --git a/adb/Android.mk b/adb/Android.mk
index 7cfbcb9..8d38077 100644
--- a/adb/Android.mk
+++ b/adb/Android.mk
@@ -199,7 +199,7 @@
 LOCAL_CFLAGS += -DALLOW_ADBD_ROOT=1
 endif
 
-ifneq (,$(filter userdebug,$(TARGET_BUILD_VARIANT)))
+ifneq (,$(filter userdebug eng,$(TARGET_BUILD_VARIANT)))
 LOCAL_CFLAGS += -DALLOW_ADBD_DISABLE_VERITY=1
 endif