What is SYCL 1.2?

It is optional step so you can skip if you want.

OpenCL (Open Computing Language) is a framework for writing programs that execute across heterogeneous platforms consisting of central processing units (CPUs), graphics processing units (GPUs), digital signal processors (DSPs), field-programmable gate arrays (FPGAs) and other processors or hardware accelerators.

so if you want to intall you have to Setting Up TensorFlow With OpenCL Using SYCL bellow link provide step by step information about it https://developer.codeplay.com/computecppce/latest/getting-started-with-tensorflow

SYCL is a C++ abstraction layer for OpenCL. TensorFlow's experimental support for OpenCL uses SYCL, in conjunction with a SYCL-aware C++ compiler.

As Yaroslav pointed out in his comment, SYCL is only required if you are building TensorFlow with OpenCL support. The following question during the execution of ./configure asks about OpenCL support:

Do you wish to build TensorFlow with OpenCL support? [y/N]

If you answer N, you will not have to supply a SYCL path.