Add UR_EXTERNAL_DEPENDENCIES CMake option (#17291)

The `UR_EXTERNAL_DEPENDENCIES` option can be used to specify a list of
CMake targets that all libraries and executables in the UR build should
depend on, e.g. the `sycl-headers` target.

Following on from intel/llvm#17093

Author: kbenzie

CMakeLists.txt

@@ -48,6 +48,8 @@ option(UR_BUILD_XPTI_LIBS "Build the XPTI libraries when tracing is enabled" ON)
 option(UR_STATIC_LOADER "Build loader as a static library" OFF)
 option(UR_FORCE_LIBSTDCXX "Force use of libstdc++ in a build using libc++ on Linux" OFF)
 option(UR_ENABLE_LATENCY_HISTOGRAM "Enable latncy histogram" OFF)
+set(UR_EXTERNAL_DEPENDENCIES "" CACHE LIST
+    "List of external CMake targets for executables/libraries to depend on")
 set(UR_DPCXX "" CACHE FILEPATH "Path of the DPC++ compiler executable")
 set(UR_DPCXX_BUILD_FLAGS "" CACHE STRING "Build flags to pass to DPC++ when compiling device programs")
 set(UR_SYCL_LIBRARY_DIR "" CACHE PATH

cmake/helpers.cmake

@@ -191,6 +191,9 @@ function(add_ur_executable name)
     add_ur_target_compile_options(${name})
     add_ur_target_exec_options(${name})
     add_ur_target_link_options(${name})
+    if(UR_EXTERNAL_DEPENDENCIES)
+        add_dependencies(${name} ${UR_EXTERNAL_DEPENDENCIES})
+    endif()
 endfunction()
 
 function(add_ur_library name)
@@ -202,6 +205,9 @@ function(add_ur_library name)
             $<$<STREQUAL:$<TARGET_LINKER_FILE_NAME:${name}>,link.exe>:LINKER:/DEPENDENTLOADFLAG:0x2000>
         )
     endif()
+    if(UR_EXTERNAL_DEPENDENCIES)
+        add_dependencies(${name} ${UR_EXTERNAL_DEPENDENCIES})
+    endif()
 endfunction()
 
 function(install_ur_library name)