envsetup: use $(CURDIR) for getting current directory

Change-Id: I5f00faf64ec31d86dd2e48ec038748ce8499380b
Add support for cross compiling Windows tools on Darwin.

Change-Id: I71372543e8da02e1d2437d6da7eb46b0a72c9870
Merge branch 'cm-10.1' of github.com:CyanogenMod/android_build into cm-10.1