Fix CI job (#73)

Summary:
Pull Request resolved: #73

Apparently in macos CI, python3 and python are pointing to different python environment.

python3 -> /Library/Python/3.9/site-packages/

python -> /Users/ec2-user/runner/_work/_temp/miniconda/lib/python3.9/site-packages

This diff is fixing the CI failure:
```
[2023-08-17T02:59:12.739+00:00] Local command: env -- "ASAN_OPTIONS=detect_leaks=0,detect_odr_violation=0" "GEN_DIR=GEN_DIR_DEPRECATED" "OUT=././../out" "SRCDIR=./." "SRCS=././link_torch.sh" /usr/bin/env bash -e buck-out/v2/gen/root/213ed1b7ab869379/third-party/__libtorch_gen__/sh/genrule.sh
[2023-08-17T02:59:12.739+00:00] Stdout: Error: /Library/Python/3.9/site-packages/torch/lib/libtorch.dylib doesn't exist
```

Also adding `tomli` as a ci requirements due to the following error:
```
Error:
Traceback (most recent call last):
  File "/Users/ec2-user/runner/_work/executorch/executorch/pytorch/executorch/build/extract_sources.py", line 18, in <module>
    import tomllib  # Standard in 3.11 and later
ModuleNotFoundError: No module named 'tomllib'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/ec2-user/runner/_work/executorch/executorch/pytorch/executorch/build/extract_sources.py", line 20, in <module>
    import tomli as tomllib
ModuleNotFoundError: No module named 'tomli'

CMake Error at CMakeLists.txt:101 (message):
  executorch: source list generation failed
```

Reviewed By: huydhn, cccclai

Differential Revision: D48423480

fbshipit-source-id: 39e864a834920dac93fbd479705ad4bdb67516ac

Author: larryliu0820

.github/workflows/pull.yml

@@ -51,7 +51,7 @@ jobs:
         bash .ci/scripts/test.sh
 
         # Test custom ops
-        bash examples/custom_ops/test_custom_ops.sh buck2
+        PYTHON_EXECUTABLE=python bash examples/custom_ops/test_custom_ops.sh buck2
         popd
 
   cmake-build-test-linux:
@@ -90,5 +90,5 @@ jobs:
         bash .ci/scripts/setup-macos.sh
 
         # Build and test custom ops
-        bash examples/custom_ops/test_custom_ops.sh cmake
+        PYTHON_EXECUTABLE=python bash examples/custom_ops/test_custom_ops.sh cmake
         popd

CMakeLists.txt

@@ -62,6 +62,9 @@ endif()
 if(NOT BUCK2)
   set(BUCK2 buck2)
 endif()
+if(NOT PYTHON_EXECUTABLE)
+  set(PYTHON_EXECUTABLE python3)
+endif()
 
 # TODO(dbort): Fix these warnings and remove this flag.
 set(_common_compile_options -Wno-deprecated-declarations)

examples/custom_ops/test_custom_ops.sh

@@ -14,7 +14,7 @@ set -e
 test_buck2_custom_op_1() {
   local model_name='custom_ops_1'
   echo "Exporting ${model_name}.pte"
-  python -m "examples.custom_ops.${model_name}"
+  ${PYTHON_EXECUTABLE} -m "examples.custom_ops.${model_name}"
   # should save file custom_ops_1.pte
 
   echo 'Running executor_runner'
@@ -29,7 +29,7 @@ test_buck2_custom_op_1() {
 test_cmake_custom_op_1() {
   local model_name='custom_ops_1'
   echo "Exporting ${model_name}.pte"
-  python -m "examples.custom_ops.${model_name}"
+  ${PYTHON_EXECUTABLE} -m "examples.custom_ops.${model_name}"
   # should save file custom_ops_1.pte
   (rm -rf cmake-out \
     && mkdir cmake-out \
@@ -50,7 +50,7 @@ test_buck2_custom_op_2() {
   SO_LIB=$(buck2 build //examples/custom_ops:custom_ops_aot_lib_2 --show-output | grep "buck-out" | cut -d" " -f2)
 
   echo "Exporting ${model_name}.pte"
-  python -m "examples.custom_ops.${model_name}" --so_library="$SO_LIB"
+  ${PYTHON_EXECUTABLE} -m "examples.custom_ops.${model_name}" --so_library="$SO_LIB"
   # should save file custom_ops_2.pte
 
   buck2 run //examples/executor_runner:executor_runner \
@@ -77,7 +77,7 @@ get_shared_lib_ext() {
 
 test_cmake_custom_op_2() {
   local model_name='custom_ops_2'
-  SITE_PACKAGES="$(python -c 'from distutils.sysconfig import get_python_lib; print(get_python_lib())')"
+  SITE_PACKAGES="$(${PYTHON_EXECUTABLE} -c 'from distutils.sysconfig import get_python_lib; print(get_python_lib())')"
   CMAKE_PREFIX_PATH="${SITE_PACKAGES}/torch"
 
   (rm -rf cmake-out \
@@ -92,13 +92,17 @@ test_cmake_custom_op_2() {
 
   EXT=$(get_shared_lib_ext)
   echo "Exporting ${model_name}.pte"
-  python -m "examples.custom_ops.${model_name}" --so_library="cmake-out/examples/custom_ops/libcustom_ops_aot_lib$EXT"
+  ${PYTHON_EXECUTABLE} -m "examples.custom_ops.${model_name}" --so_library="cmake-out/examples/custom_ops/libcustom_ops_aot_lib$EXT"
   # should save file custom_ops_2.pte
 
   echo 'Running executor_runner'
   cmake-out/executor_runner "--model_path=./${model_name}.pte"
 }
 
+if [[ -z $PYTHON_EXECUTABLE ]];
+then
+  PYTHON_EXECUTABLE=python3
+fi
 if [[ $1 == "cmake" ]];
 then
   test_cmake_custom_op_1

third-party/link_torch.sh

@@ -33,7 +33,7 @@ while getopts ":o:f:" opt; do
   esac
 done
 
-LIB=$(python3 -c 'from distutils.sysconfig import get_python_lib; print(get_python_lib())')
+LIB=$(python -c 'from distutils.sysconfig import get_python_lib; print(get_python_lib())')
 
 # delimiter ,
 export IFS=","