OSL: Add ACPI_APITS and re-enables AAPITS builds.

Newly added portable OSLs are useful for EFI porting, but tests didn't
cover AAPITS, now AAPITS build is broken.
This patch re-enables AAPITS build. This patch also adds ACPI_APITS
definition so that if we have troubles in sharing code between AAPITS and
ACPI_EXEC_APP, we now have means to introduce differntiations. Lv Zheng.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Merge pull request #40 from zetalog/acpica-cygwin

Acpica cygwin