Properly export ET_USE_THREADPOOL from the threadpool extension (#8947)

We had a bunch of targets that would define this macro ad-hoc. It's supposed to indicate that the threadpool extension is available, so just make sure that we have it as a PUBLIC target_compile_definition in CMake and an exported_preprocessor_flags entry in Buck for extension_threadpool.

Test Plan: CI on following NOCOMMIT PR, which fails builds if ET_USE_THREADPOOL is not defined in affected places.

Needed for #8932.

Author: swolchok

build/executorch-config.cmake

@@ -141,3 +141,6 @@ if(TARGET cpublas)
     cpublas PROPERTIES INTERFACE_LINK_LIBRARIES extension_parallel
   )
 endif()
+if(TARGET extension_threadpool)
+  target_compile_definitions(extension_threadpool INTERFACE ET_USE_THREADPOOL)
+endif()

examples/models/llama/CMakeLists.txt

@@ -131,7 +131,6 @@ endif()
 set(XNNPACK_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/../../../backends/xnnpack)
 # Extra compile option and include dir for pthreadpool
 if(EXECUTORCH_BUILD_PTHREADPOOL)
-  list(APPEND _common_compile_options -DET_USE_THREADPOOL)
   list(APPEND link_libraries extension_threadpool pthreadpool)
   list(APPEND _common_include_directories
        ${XNNPACK_ROOT}/third-party/pthreadpool/include

examples/models/llava/CMakeLists.txt

@@ -130,7 +130,6 @@ endif()
 set(XNNPACK_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/../../../backends/xnnpack)
 # Extra compile option and include dir for pthreadpool
 if(EXECUTORCH_BUILD_PTHREADPOOL)
-  list(APPEND _common_compile_options -DET_USE_THREADPOOL)
   list(APPEND link_libraries extension_threadpool pthreadpool)
   list(APPEND _common_include_directories
        ${XNNPACK_ROOT}/third-party/pthreadpool/include

examples/models/llava/targets.bzl

@@ -7,9 +7,6 @@ def define_common_targets():
             "main.cpp",
         ],
         compiler_flags = ["-Wno-global-constructors"],
-        preprocessor_flags = [
-            "-DET_USE_THREADPOOL",
-        ],
         deps = [
             "//executorch/examples/models/llava/runner:runner",
             "//executorch/extension/evalue_util:print_evalue",

extension/android/CMakeLists.txt

@@ -119,7 +119,6 @@ if(EXECUTORCH_BUILD_KERNELS_CUSTOM)
 endif()
 
 if(TARGET pthreadpool)
-  target_compile_definitions(executorch_jni PRIVATE ET_USE_THREADPOOL=1)
   target_include_directories(
     executorch_jni
     PUBLIC

extension/llm/custom_ops/CMakeLists.txt

@@ -78,7 +78,7 @@ target_include_directories(
 target_link_libraries(custom_ops PUBLIC ${custom_ops_libs} executorch_core)
 
 target_compile_options(
-  custom_ops PUBLIC ${_common_compile_options} -DET_USE_THREADPOOL
+  custom_ops PUBLIC ${_common_compile_options}
 )
 
 install(TARGETS custom_ops DESTINATION lib)
@@ -130,7 +130,7 @@ if(EXECUTORCH_BUILD_KERNELS_CUSTOM_AOT)
   target_compile_options(
     custom_ops_aot_lib
     PUBLIC -Wno-deprecated-declarations -fPIC -frtti -fexceptions
-           ${_common_compile_options} -DET_USE_THREADPOOL
+           ${_common_compile_options}
   )
 
   install(TARGETS custom_ops_aot_lib

extension/threadpool/CMakeLists.txt

@@ -32,6 +32,7 @@ target_include_directories(
   PUBLIC ${EXECUTORCH_ROOT}/backends/xnnpack/third-party/cpuinfo/include
          ${EXECUTORCH_ROOT}/backends/xnnpack/third-party/pthreadpool/include
 )
+target_compile_definitions(extension_threadpool PUBLIC ET_USE_THREADPOOL)
 target_compile_options(extension_threadpool PUBLIC ${_common_compile_options})
 
 # Install libraries