Implement JIT Source and JIT Defines into the SYCL backend

[jrwrigh]

This may be useful to add as well:

libCEED/backends/cuda/ceed-cuda-compile.cpp

Lines 87 to 113 in 6001dc9

	{
	const char **jit_source_dirs;
	CeedCallBackend(CeedGetJitSourceRoots(ceed, &num_jit_source_dirs, &jit_source_dirs));
	CeedCallBackend(CeedRealloc(num_opts + num_jit_source_dirs, &opts));
	for (CeedInt i = 0; i < num_jit_source_dirs; i++) {
	std::ostringstream include_dir_arg;
	include_dir_arg << "-I" << jit_source_dirs[i];
	CeedCallBackend(CeedStringAllocCopy(include_dir_arg.str().c_str(), (char **)&opts[num_opts + i]));
	}
	CeedCallBackend(CeedRestoreJitSourceRoots(ceed, &jit_source_dirs));
	}
	// User defines
	{
	const char **jit_defines;
	CeedCallBackend(CeedGetJitDefines(ceed, &num_jit_defines, &jit_defines));
	CeedCallBackend(CeedRealloc(num_opts + num_jit_source_dirs + num_jit_defines, &opts));
	for (CeedInt i = 0; i < num_jit_defines; i++) {
	std::ostringstream define_arg;
	define_arg << "-D" << jit_defines[i];
	CeedCallBackend(CeedStringAllocCopy(define_arg.str().c_str(), (char **)&opts[num_opts + num_jit_source_dirs + i]));
	}
	CeedCallBackend(CeedRestoreJitDefines(ceed, &jit_defines));
	}

Originally posted by @jeremylt in #1840 (comment)