[SYCL][E2E] Fix error reporting in e2e lit config (#18535)

Checking the output of `get_sycl_ls_verbose` expected the function to
update a global `sp` variable. Since it didn't do that, this resulted
in an error when trying to print the command output.

This patch changes the function to return the subprocess directly, which
is used during error message generation.

Author: RossBrunton

sycl/test-e2e/lit.cfg.py

@@ -864,7 +864,7 @@ def get_sycl_ls_verbose(sycl_device, env):
                 f"stdout:{sp.stdout}\n"
                 f"stderr:{sp.stderr}\n"
             )
-        return sp.stdout.splitlines()
+        return sp
 
 
 # A device filter such as level_zero:gpu can have multiple devices under it and
@@ -893,7 +893,7 @@ def get_sycl_ls_verbose(sycl_device, env):
 
     platform_devices = remove_level_zero_suffix(backend + ":*")
 
-    for line in get_sycl_ls_verbose(platform_devices, env):
+    for line in get_sycl_ls_verbose(platform_devices, env).stdout.splitlines():
         if re.match(r" *Architecture:", line):
             _, architecture = line.strip().split(":", 1)
             detected_architectures.append(architecture.strip())
@@ -952,7 +952,8 @@ def get_sycl_ls_verbose(sycl_device, env):
     # See format.py's parse_min_intel_driver_req for explanation.
     is_intel_driver = False
     intel_driver_ver = {}
-    for line in get_sycl_ls_verbose(sycl_device, env):
+    sycl_ls_sp = get_sycl_ls_verbose(sycl_device, env)
+    for line in sycl_ls_sp.stdout.splitlines():
         if re.match(r" *Vendor *: Intel\(R\) Corporation", line):
             is_intel_driver = True
         if re.match(r" *Driver *:", line):
@@ -989,7 +990,7 @@ def get_sycl_ls_verbose(sycl_device, env):
     if dev_aspects == []:
         lit_config.error(
             "Cannot detect device aspect for {}\nstdout:\n{}\nstderr:\n{}".format(
-                sycl_device, sp.stdout, sp.stderr
+                sycl_device, sycl_ls_sp.stdout, sycl_ls_sp.stderr
             )
         )
         dev_aspects.append(set())
@@ -1001,7 +1002,7 @@ def get_sycl_ls_verbose(sycl_device, env):
     if dev_sg_sizes == []:
         lit_config.error(
             "Cannot detect device SG sizes for {}\nstdout:\n{}\nstderr:\n{}".format(
-                sycl_device, sp.stdout, sp.stderr
+                sycl_device, sycl_ls_sp.stdout, sycl_ls_sp.stderr
             )
         )
         dev_sg_sizes.append(set())
@@ -1024,7 +1025,7 @@ def get_sycl_ls_verbose(sycl_device, env):
             if not config.allow_unknown_arch:
                 lit_config.error(
                     "Cannot detect architecture for {}\nstdout:\n{}\nstderr:\n{}".format(
-                        sycl_device, sp.stdout, sp.stderr
+                        sycl_device, sycl_ls_sp.stdout, sycl_ls_sp.stderr
                     )
                 )
             architectures = set()