build: explicitly specify the python path

This ensures that we use python 2.7 when building LLVM.  The LLVM
tooling has not yet been ported to python 3, and this breaks the CI
builds which are now finding python 3 via `PATH`.

Author: compnerd

utils/build-script-impl

@@ -669,6 +669,10 @@ function set_build_options_for_host() {
                 -DCOMPILER_RT_ENABLE_TVOS:BOOL=FALSE
                 -DSANITIZER_MIN_OSX_VERSION="${cmake_osx_deployment_target}"
                 -DLLVM_ENABLE_MODULES:BOOL="$(true_false ${LLVM_ENABLE_MODULES})"
+                # NOTE(compnerd) this explicitly sets up the python executable
+                # since we sometimes end up with python 3 and the tooling
+                # currently relies on python 2.7
+                -DPYTHON_EXECUTABLE:PATH=/usr/bin/python2.7
             )
             if [[ $(is_llvm_lto_enabled) == "TRUE" ]]; then
                 if [[ $(cmake_needs_to_specify_standard_computed_defaults) == "TRUE" ]]; then
@@ -2558,6 +2562,21 @@ for host in "${ALL_HOSTS[@]}"; do
                     cmake_options+=(
                       -DLLDB_CODESIGN_IDENTITY=""
                       -DLLDB_USE_SYSTEM_DEBUGSERVER:BOOL="${LLDB_USE_SYSTEM_DEBUGSERVER}"
+
+                      # NOTE(compnerd) this explicitly sets up the python
+                      # executable since we sometimes end up with python 3 and
+                      # the tooling currently relies on python 2.7
+                      -DPython_ADDITIONAL_VERSIONS="2.7"
+                      -DPYTHON_EXECUTABLE:PATH=/usr/bin/python2.7
+                      -DPYTHON_LIBRARY="$(xcrun --sdk ${xcrun_sdk_name} --show-sdk-path)/System/Library/Frameworks/Python.framework/Versions/2.7/lib/libpython2.7.tbd"
+                      -DPYTHON_INCLUDE_DIR="$(xcrun --sdk ${xcrun_sdk_name} --show-sdk-path)/System/Library/Frameworks/Python.framework/Headers"
+                    )
+                  else
+                    cmake_options+=(
+                      # NOTE(compnerd) this explicitly sets up the python
+                      # executable since we sometimes end up with python 3 and
+                      # the tooling currently relies on python 2.7
+                      -DPYTHON_EXECUTABLE:PATH=/usr/bin/python2.7
                     )
                   fi
                 fi