cmake,get_asm_obj_format: use win32/win64 w/cygwin

this matches msys and the selection in libvpx

based on original patch from ktim94 <at> gmail

Bug: aomedia:2994
Change-Id: Id23390561cfaa5d54b3bb682b869ebb05ec4601f
(cherry picked from commit 4eec0a807b820726e1778debe9d1111bceafaea1)

build/cmake/aom_optimization.cmake

diff --git a/build/cmake/aom_optimization.cmake b/build/cmake/aom_optimization.cmake
index d8b258f..e4b29de 100644
--- a/build/cmake/aom_optimization.cmake
+++ b/build/cmake/aom_optimization.cmake
@@ -100,6 +100,7 @@
     if("${AOM_TARGET_SYSTEM}" STREQUAL "Darwin")
       set(objformat "macho64")
     elseif("${AOM_TARGET_SYSTEM}" STREQUAL "MSYS"
+           OR "${AOM_TARGET_SYSTEM}" STREQUAL "CYGWIN"
            OR "${AOM_TARGET_SYSTEM}" STREQUAL "Windows")
       set(objformat "win64")
     else()
@@ -109,6 +110,7 @@
     if("${AOM_TARGET_SYSTEM}" STREQUAL "Darwin")
       set(objformat "macho32")
     elseif("${AOM_TARGET_SYSTEM}" STREQUAL "MSYS"
+           OR "${AOM_TARGET_SYSTEM}" STREQUAL "CYGWIN"
            OR "${AOM_TARGET_SYSTEM}" STREQUAL "Windows")
       set(objformat "win32")
     else()