Build speed up : out directory changed to SSD

Link:
New experimental build system feature: out/ directories in another location
http://groups.google.com/group/android-building/browse_thread/thread/ca6c1648aa52acb9

This should be useful when storing the build output on a physically
different volume. Additional benefits might come from using a
dedicated volume for that where journaling is disabled, and/or from
using an SSD.

To use it, set the OUT_DIR_COMMON_BASE environment to the directory
where the output directories will be created. A subdirectory will be
created there for each source tree. The name of the subdirectory
matches that of the source tree.

memo:
- we can change "out directory" with OUT_DIR_COMMON_BASE
- use SSD to build speed up.

but, This patch is commited in Master blanch, so is not in Android-4.0.3_r1 blanch.

check it !!
\build\core\envsetup.mk

# ---------------------------------------------------------------
# figure out the output directories

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

DEBUG_OUT_DIR := $(OUT_DIR)/debug