Fix oneTBB flags for Windows SYCL clang builds

Author: allnes

3rdparty/CMakeLists.txt

@@ -10,7 +10,18 @@ option(TBB_EXAMPLES "Build TBB examples" OFF)
 set(TBB_STRICT OFF CACHE BOOL "Treat compiler warnings as errors")
 
 # Configure TBB with unified settings
+set(_itlabai_restore_msvc FALSE)
+if(ITLABAI_ENABLE_SYCL AND WIN32 AND CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
+   CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC" AND NOT MSVC)
+    # oneTBB keys off MSVC here; clang++ with the MSVC target otherwise gets
+    # non-Windows flags such as -fPIC.
+    set(_itlabai_restore_msvc TRUE)
+    set(MSVC TRUE)
+endif()
 add_subdirectory(TBB)
+if(_itlabai_restore_msvc)
+    unset(MSVC)
+endif()
 
 # Create a unified TBB interface target
 if(NOT TARGET TBB_unified)