[SYCL] Require building with zstd library

SYCL device image compression requires zstd.
Running `clang++ -fsycl --offload-compress` with a version of the
compiler compiled without zstd leads to an error.
Instead of complicating the handling of device image compression to also
make it optional, it's cleaner to avoid compiling without zstd library,
and to make it a required dependency for SYCL.
Using LLVM_ENABLE_ZSTD=FORCE_ON prevents from compiling without zstd.

Author: ph0b

Diff for: buildbot/configure.py

@@ -64,7 +64,6 @@ def do_configure(args, passthrough_args):
 
     sycl_enable_xpti_tracing = "ON"
     xpti_enable_werror = "OFF"
-    llvm_enable_zstd = "ON"
     spirv_enable_dis = "OFF"
 
     if sys.platform != "darwin":
@@ -188,7 +187,7 @@ def do_configure(args, passthrough_args):
         "-DLLVM_ENABLE_PROJECTS={}".format(llvm_enable_projects),
         "-DSYCL_BUILD_PI_HIP_PLATFORM={}".format(sycl_build_pi_hip_platform),
         "-DLLVM_BUILD_TOOLS=ON",
-        "-DLLVM_ENABLE_ZSTD={}".format(llvm_enable_zstd),
+        "-DLLVM_ENABLE_ZSTD=FORCE_ON",  # Required by SYCL device image compression.
         "-DLLVM_USE_STATIC_ZSTD=ON",
         "-DSYCL_ENABLE_WERROR={}".format(sycl_werror),
         "-DCMAKE_INSTALL_PREFIX={}".format(install_dir),