Use OUT_DIR_COMMON_BASE if OUT_DIR is unset.

In build/make/core/envsetup.mk the logic for setting OUT_DIR is this:

ifeq (,$(strip $(OUT_DIR)))
ifeq (,$(strip $(OUT_DIR_COMMON_BASE)))
OUT_DIR := $(TOPDIR)out
else
OUT_DIR := $(OUT_DIR_COMMON_BASE)/$(notdir $(PWD))
endif
endif

To get the correct value for its out_dir variable, buildbot-build.sh
needs to do the same, otherwise it'll generate incorrect target names
in environments where OUT_DIR_COMMON_BASE is set but OUT_DIR unset.

Test: art/tools/buildbot-build.sh --host

Change-Id: I558949655a97b47ce3c560ed70310c9768e1da5c
diff --git a/tools/buildbot-build.sh b/tools/buildbot-build.sh
index 12e0338..2d26b48 100755
--- a/tools/buildbot-build.sh
+++ b/tools/buildbot-build.sh
@@ -19,7 +19,17 @@
   exit 1
 fi
 
-out_dir=${OUT_DIR-out}
+# Logic for setting out_dir from build/make/core/envsetup.mk:
+if [[ -z $OUT_DIR ]]; then
+  if [[ -z $OUT_DIR_COMMON_BASE ]]; then
+    out_dir=out
+  else
+    out_dir=${OUT_DIR_COMMON_BASE}/${PWD##*/}
+  fi
+else
+  out_dir=${OUT_DIR}
+fi
+
 java_libraries_dir=${out_dir}/target/common/obj/JAVA_LIBRARIES
 common_targets="vogar core-tests apache-harmony-jdwp-tests-hostdex jsr166-tests mockito-target ${out_dir}/host/linux-x86/bin/jack"
 mode="target"