CMake: Make the path to the Clang tool configurable

Set `SAPI_CLANG_TOOL_EXECUTABLE` to specify the location of a pre-built Clang
tool based header generator.

PiperOrigin-RevId: 531425738
Change-Id: I723d19122cc738d9906c8c568d156d44c58d9746

cmake/SapiBuildDefs.cmake

@@ -155,8 +155,12 @@ function(add_sapi_library)
   if(SAPI_ENABLE_CLANG_TOOL)
     set(_sapi_isystem_args ${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES})
     list(TRANSFORM _sapi_isystem_args PREPEND --extra-arg-before=-isystem)
+    if(SAPI_CLANG_TOOL_EXECUTABLE)
+      list(APPEND _sapi_generator_command "${SAPI_CLANG_TOOL_EXECUTABLE}")
+    else()
+      list(APPEND _sapi_generator_command sapi_generator_tool)
+    endif()
     list(APPEND _sapi_generator_command
-      sapi_generator_tool
       -p "${CMAKE_CURRENT_BINARY_DIR}"
       ${_sapi_generator_args}
       ${_sapi_isystem_args}

cmake/SapiDeps.cmake

@@ -95,7 +95,13 @@ endif()
 
 find_package(Threads REQUIRED)
 
-if(NOT SAPI_ENABLE_CLANG_TOOL)
+if(SAPI_ENABLE_CLANG_TOOL)
+  # If unset (the default), CMake will build the tool first and add it as a
+  # dependency.
+  set(SAPI_CLANG_TOOL_EXECUTABLE "" CACHE FILEPATH
+    "Path to the Clang tool based header generator"
+  )
+else()
   # Find Python 3 and add its location to the cache so that its available in
   # the add_sapi_library() macro in embedding projects.
   find_package(Python3 COMPONENTS Interpreter REQUIRED)

sandboxed_api/CMakeLists.txt

@@ -15,7 +15,7 @@
 add_subdirectory(tools/filewrapper)
 add_subdirectory(sandbox2)
 add_subdirectory(util)
-if(SAPI_ENABLE_CLANG_TOOL)
+if(SAPI_ENABLE_CLANG_TOOL AND NOT SAPI_CLANG_TOOL_EXECUTABLE)
   add_subdirectory(tools/clang_generator)
 endif()
 add_subdirectory(examples)