The following enabled me to reference libwebp binaries (in case it helps someone else) for Android C++ using cmake...
target_include_directories(foo PRIVATE
../../../../libwebp/src/webp
)
if(ANDROID)
if(${ANDROID_ABI} STREQUAL "armeabi-v7a")
SET(WEBP_ANDROID_FOLDER "build-android32")
else()
SET(WEBP_ANDROID_FOLDER "build-android")
endif()
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libcpufeatures.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libexampleutil.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libextras.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libimagedec.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libimageenc.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libimageioutil.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libsharpyuv.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libwebp.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libwebpdecoder.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libwebpdemux.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/libwebpmux.a)
target_link_libraries(xgl PRIVATE ${GLOBAL_ROOT_SRC_DIR}/../libwebp/${WEBP_ANDROID_FOLDER}/cwebp)
endif()
Next I will see if I can get this reference code from @udara to write a webp file (taking a uint8_t array as input) (btw the uint8_t array is data from a vulkan VkImage's such as VK_FORMAT_R8G8B8A8_UNORM from the swapchain)