Utilize IS_ABSOLUTE CMake function instead of REGEX match for relative paths (#1129)
Utilize IS_ABSOLUTE CMake function instead of REGEX match for relative paths (#1129)

* Utilize IS_ABSOLUTE CMake function instead of REGEX match

* Address PR comments
aws/aws-iot-device-sdk-embedded-C,aws/aws-iot-device-sdk-embedded-C,aws/aws-iot-device-sdk-embedded-C