envsetup: set OUT_DIR to an absolute path always

OUT_DIR was set to $(TOPDIR)out previously,
but $(TOPDIR) was null, so it was a relative path.
This broke releasetools, inline kernel building, etc
since they require absolute paths.
Fix it so that it is set to $(shell readlink -f .)/out
if $(TOPDIR) is null.

Also remove hacks which checked if (OUT_DIR) was out
and changed it to $(ANDROID_BUILD_TOP)/out to workaround
the aforementioned problem.

Change-Id: I459a3b1325a1bbea0565cd73f6acf160d4ed9b39

core/envsetup.mk

@@ -197,8 +197,12 @@ endif
 
 ifeq (,$(strip $(OUT_DIR)))
 ifeq (,$(strip $(OUT_DIR_COMMON_BASE)))
+ifneq ($(TOPDIR),)
 OUT_DIR := $(TOPDIR)out
 else
+OUT_DIR := $(shell readlink -f .)/out
+endif
+else
 OUT_DIR := $(OUT_DIR_COMMON_BASE)/$(notdir $(PWD))
 endif
 endif