offload-tunnel-cmake with proper escape (llvm#4312)

Author: Salinas, David

llvm/runtimes/CMakeLists.txt

@@ -502,10 +502,18 @@ if(build_runtimes)
   endif()
 
   # Forward user-provived system configuration to runtimes for requirement introspection.
-  # CMAKE_PREFIX_PATH is the search path for CMake packages.
+  # CMAKE_PREFIX_PATH is the search path for CMake packages. In order to pass through
+  # the command line interface, the CMake semicolon separator needs to be replaced
+  # with $<SEMICOLON>
   if(CMAKE_PREFIX_PATH)
-    list(APPEND extra_cmake_args "-DCMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH}")
+    string(JOIN "$<SEMICOLON>" escaped_cmake_prefix_path ${CMAKE_PREFIX_PATH})
+    # Some projects require access to the LLVM lib/cmake directory
+    if (OFFLOAD_EXTERNAL_PROJECT_UNIFIED_ROCR OR DEFINED LIBOMPTARGET_EXTERNAL_PROJECT_ROCM_DEVICE_LIBS_PATH)
+      string(PREPEND escaped_cmake_prefix_path "${CMAKE_BINARY_DIR}/lib/cmake$<SEMICOLON>")
+    endif()
+    list(APPEND extra_cmake_args "-DCMAKE_PREFIX_PATH=${escaped_cmake_prefix_path}")
   endif()
+
   # CMAKE_PROGRAM_PATH is the search path for executables such as python.
   if(CMAKE_PROGRAM_PATH)
     list(APPEND extra_cmake_args "-DCMAKE_PROGRAM_PATH=${CMAKE_PROGRAM_PATH}")
@@ -522,9 +530,6 @@ if(build_runtimes)
   if("openmp" IN_LIST LLVM_ENABLE_RUNTIMES OR "offload" IN_LIST LLVM_ENABLE_RUNTIMES)
     # With ROCm 6.3 the ROCr runtime and the thunk layer share a single repository.
     # No need to provide a separate path for ROCt.
-    if (OFFLOAD_EXTERNAL_PROJECT_UNIFIED_ROCR OR DEFINED LIBOMPTARGET_EXTERNAL_PROJECT_ROCM_DEVICE_LIBS_PATH)
-      list(APPEND extra_cmake_args "-DCMAKE_PREFIX_PATH=${CMAKE_BINARY_DIR}/lib/cmake$<SEMICOLON>${CMAKE_PREFIX_PATH}")
-    endif()
     if (OFFLOAD_EXTERNAL_PROJECT_UNIFIED_ROCR)
       if(NOT DEFINED LIBOMPTARGET_EXTERNAL_PROJECT_HSA_PATH)
         message(SEND_ERROR "External ROCr requires setting LIBOMPTARGET_EXTERNAL_PROJECT_HSA_PATH")