refactor no longer needed EXECUTORCH_BUILD_HOST_TARGETS (#10320)

### Summary
Removes EXECUTORCH_BUILD_HOST_TARGETS per @mergennachin
[comment](#9306 (review)).
Fixes #9404

### Test plan
Ensure executorch and cadence builds successfully:
```
./install_executorch.sh
mkdir cmake-out
cmake -DCMAKE_TOOLCHAIN_FILE=backends/cadence/cadence.cmake \
    -DCMAKE_INSTALL_PREFIX=cmake-out \
    -DCMAKE_BUILD_TYPE=Debug \
    -DPYTHON_EXECUTABLE=python3 \
    -DEXECUTORCH_BUILD_EXTENSION_RUNNER_UTIL=ON \
    -DEXECUTORCH_BUILD_HOST_TARGETS=ON \
    -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=OFF \
    -DEXECUTORCH_BUILD_PTHREADPOOL=OFF \
    -DEXECUTORCH_BUILD_CPUINFO=OFF \
    -Bcmake-out .
cmake --build cmake-out -j8 --target install --config Debug
cmake -DCMAKE_BUILD_TYPE=Debug \
    -DCMAKE_TOOLCHAIN_FILE=examples/backends/cadence.cmake \
    -DCMAKE_PREFIX_PATH=cmake-out \
    -DMODEL_PATH=add.pte \
    -DNXP_SDK_ROOT_DIR=/home/user_name/nxp-sdk \
    -DNN_LIB_BASE_DIR=/home/user_name/nnlib-hifi4 \
    -Bcmake-out/examples/cadence \
    examples/cadence
cmake --build cmake-out/examples/cadence -j8 -t cadence_executorch_example
ls cmake-xt/*.bin
```
* Test plan assumes nxp-sdk and nnlib-hifir are in user's home directory
and Xtensa compiler is available (env vars set). See [cadence
docs](https://github.com/pytorch/executorch/blob/main/docs/source/backends-cadence.md)
* Since these are modifications to the build system, I leave it to
discretion if CI builds provide enough risk protection to merge.
* Happy to write tests if needed - I'll need a little direction here if
needed. #9306 ran `./install_executorch.sh`, `build_apple_frameworks.sh`
and `build_android_library.sh`.

---------

Co-authored-by: Mergen Nachin <[email protected]>

Author: bvanderhaar

CMakeLists.txt

@@ -410,20 +410,6 @@ endif()
 message(STATUS "executorch: Using sources file ${EXECUTORCH_SRCS_FILE}")
 include(${EXECUTORCH_SRCS_FILE})
 
-#
-# Modify default options when cross-compiling.
-#
-# The intent is for the EXECUTORCH_BUILD_HOST_TARGETS option to affect the
-# default ON/OFF values of host targets around the tree. This way, a user can
-# disable EXECUTORCH_BUILD_HOST_TARGETS to disable all host targets, and then
-# optionally re-enable some of those targets. Or they could leave
-# EXECUTORCH_BUILD_HOST_TARGETS enabled and then optionally disable any given
-# host target.
-#
-# We can then use various cross-compilation hints to set the default value of
-# EXECUTORCH_BUILD_HOST_TARGETS, which can still be overridden if desired.
-#
-
 # Detect if an iOS toolchain is set.
 if(CMAKE_TOOLCHAIN_FILE MATCHES ".*(iOS|ios\.toolchain)\.cmake$")
   set(CMAKE_TOOLCHAIN_IOS ON)
@@ -458,16 +444,6 @@ if(EXECUTORCH_USE_CPP_CODE_COVERAGE)
   endif()
 endif()
 
-# EXECUTORCH_BUILD_HOST_TARGETS: Option to control the building of host-only
-# tools like `flatc`, along with example executables like `executor_runner` and
-# libraries that it uses, like `gflags`. Disabling this can be helpful when
-# cross-compiling, but some required tools that would have been built need to be
-# provided directly.
-cmake_dependent_option(
-  EXECUTORCH_BUILD_HOST_TARGETS "Build host-only targets." ON
-  "NOT CMAKE_TOOLCHAIN_IOS" OFF
-)
-
 #
 # flatc: Flatbuffer commandline tool to generate .h files from .fbs files
 #
@@ -665,10 +641,7 @@ add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/configurations)
 #
 # gflags: Commandline flag host library.
 #
-cmake_dependent_option(
-  EXECUTORCH_BUILD_GFLAGS "Build the gflags library." ON
-  EXECUTORCH_BUILD_HOST_TARGETS OFF
-)
+option(EXECUTORCH_BUILD_GFLAGS "Build the gflags library." ON)
 if(EXECUTORCH_BUILD_GFLAGS)
   add_subdirectory(third-party/gflags)
 endif()
@@ -692,10 +665,7 @@ install(FILES tools/cmake/executorch-config.cmake DESTINATION lib/cmake/ExecuTor
 #
 # executor_runner: Host tool that demonstrates program execution.
 #
-cmake_dependent_option(
-  EXECUTORCH_BUILD_EXECUTOR_RUNNER "Build the executor_runner executable" ON
-  EXECUTORCH_BUILD_HOST_TARGETS OFF
-)
+option(EXECUTORCH_BUILD_EXECUTOR_RUNNER "Build the executor_runner executable" ON)
 
 # Add googletest if any test targets should be built
 if(BUILD_TESTING)

backends/cadence/build_cadence_fusionG3.sh

@@ -40,7 +40,6 @@ if $STEPWISE_BUILD; then
         -DCMAKE_TOOLCHAIN_FILE=/home/zonglinpeng/ws/zonglinpeng/executorch/backends/cadence/cadence.cmake \
         -DCMAKE_INSTALL_PREFIX=cmake-out \
         -DCMAKE_BUILD_TYPE=Release \
-        -DEXECUTORCH_BUILD_HOST_TARGETS=ON \
         -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=ON \
         -DEXECUTORCH_BUILD_PTHREADPOOL=OFF \
         -DEXECUTORCH_BUILD_CADENCE=ON \
@@ -65,7 +64,6 @@ else
         -DCMAKE_TOOLCHAIN_FILE=./backends/cadence/cadence.cmake \
         -DCMAKE_INSTALL_PREFIX=cmake-out \
         -DCMAKE_BUILD_TYPE=Release \
-        -DEXECUTORCH_BUILD_HOST_TARGETS=ON \
         -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=ON \
         -DEXECUTORCH_BUILD_PTHREADPOOL=OFF \
         -DEXECUTORCH_BUILD_CPUINFO=OFF \

backends/cadence/build_cadence_hifi4.sh

@@ -39,7 +39,6 @@ if $STEPWISE_BUILD; then
         -DCMAKE_TOOLCHAIN_FILE=./backends/cadence/cadence.cmake \
         -DCMAKE_INSTALL_PREFIX=cmake-out \
         -DCMAKE_BUILD_TYPE=Release \
-        -DEXECUTORCH_BUILD_HOST_TARGETS=ON \
         -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=ON \
         -DEXECUTORCH_BUILD_PTHREADPOOL=OFF \
         -DEXECUTORCH_BUILD_CADENCE=ON \
@@ -63,7 +62,6 @@ else
         -DCMAKE_TOOLCHAIN_FILE=./backends/cadence/cadence.cmake \
         -DCMAKE_INSTALL_PREFIX=cmake-out \
         -DCMAKE_BUILD_TYPE=Release \
-        -DEXECUTORCH_BUILD_HOST_TARGETS=ON \
         -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=ON \
         -DEXECUTORCH_BUILD_PTHREADPOOL=OFF \
         -DEXECUTORCH_BUILD_CPUINFO=OFF \

docs/source/backends-cadence.md

@@ -170,7 +170,6 @@ cmake -DCMAKE_TOOLCHAIN_FILE=<path_to_executorch>/backends/cadence/cadence.cmake
     -DCMAKE_BUILD_TYPE=Debug \
     -DPYTHON_EXECUTABLE=python3 \
     -DEXECUTORCH_BUILD_EXTENSION_RUNNER_UTIL=ON \
-    -DEXECUTORCH_BUILD_HOST_TARGETS=ON \
     -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=OFF \
     -DEXECUTORCH_BUILD_PTHREADPOOL=OFF \
     -DEXECUTORCH_BUILD_CPUINFO=OFF \

tools/cmake/Utils.cmake

@@ -93,9 +93,6 @@ function(executorch_print_configuration_summary)
     STATUS
       "  EXECUTORCH_BUILD_GFLAGS                : ${EXECUTORCH_BUILD_GFLAGS}"
   )
-  message(STATUS "  EXECUTORCH_BUILD_HOST_TARGETS          : "
-                 "${EXECUTORCH_BUILD_HOST_TARGETS}"
-  )
   message(STATUS "  EXECUTORCH_BUILD_KERNELS_CUSTOM        : "
                  "${EXECUTORCH_BUILD_KERNELS_CUSTOM}"
   )