mksh: add mkshrc when using TW_USE_TOOLBOX

Fixes broken shell prompt in Terminal and adb shell

Before: https://del.dog/7vphlkc
After: https://del.dog/vhkjgo8

Add as prebuilt with suffix "_twrp" to avoid conflict
with original mkshrc and rename via POST_INSTALL_CMD

Prebuilt version adjusts TMPDIR variable from
"/data/local/tmp" to "/tmp" for TWRP

Change-Id: I42a1b2a8c114f66dbe659c07485f1dfae8a5d314
diff --git a/prebuilt/Android.mk b/prebuilt/Android.mk
index 235b77c..9333262 100644
--- a/prebuilt/Android.mk
+++ b/prebuilt/Android.mk
@@ -491,6 +491,18 @@
 	include $(BUILD_PREBUILT)
 endif
 
+ifeq ($(TW_USE_TOOLBOX), true)
+    include $(CLEAR_VARS)
+    LOCAL_MODULE := mkshrc_twrp
+    LOCAL_MODULE_TAGS := eng
+    LOCAL_MODULE_CLASS := ETC
+    LOCAL_MODULE_PATH := $(TARGET_RECOVERY_ROOT_OUT)/etc
+    LOCAL_SRC_FILES := $(LOCAL_MODULE)
+    LOCAL_POST_INSTALL_CMD := \
+        $(hide) mv $(TARGET_RECOVERY_ROOT_OUT)/etc/mkshrc_twrp $(TARGET_RECOVERY_ROOT_OUT)/etc/mkshrc
+    include $(BUILD_PREBUILT)
+endif
+
 #TWRP App "placeholder"
 include $(CLEAR_VARS)
 LOCAL_MODULE := me.twrp.twrpapp.apk