Bug 1720820 - Remove python executable configuration from clang build script. r=firefox-build-system-reviewers,andi

Clang >= 11 ignores PYTHON_EXECUTABLE entirely (and uses python3, which
is not even what we pass, but that's actually fine), and all the build
tasks we have on older versions find the python executable they need on
their own.

Differential Revision: https://phabricator.services.mozilla.com/D120049

build/build-clang/build-clang.py

@@ -215,7 +215,6 @@ def build_one_stage(
     osx_cross_compile,
     build_type,
     assertions,
-    python_path,
     libcxx_include_dir,
     build_wasm,
     compiler_rt_source_dir=None,
@@ -263,7 +262,6 @@ def build_one_stage(
             "-DCMAKE_INSTALL_PREFIX=%s" % inst_dir,
             "-DLLVM_TARGETS_TO_BUILD=%s" % machine_targets,
             "-DLLVM_ENABLE_ASSERTIONS=%s" % ("ON" if assertions else "OFF"),
-            "-DPYTHON_EXECUTABLE=%s" % slashify_path(python_path),
             "-DLLVM_TOOL_LIBCXX_BUILD=%s" % ("ON" if build_libcxx else "OFF"),
             "-DLLVM_ENABLE_BINDINGS=OFF",
         ]
@@ -711,10 +709,6 @@ if __name__ == "__main__":
         assertions = config["assertions"]
         if assertions not in (True, False):
             raise ValueError("Only boolean values are accepted for assertions.")
-    python_path = None
-    if "python_path" not in config:
-        raise ValueError("Config file needs to set python_path")
-    python_path = config["python_path"]
     ndk_dir = None
     android_targets = None
     if "android_targets" in config:
@@ -884,7 +878,6 @@ if __name__ == "__main__":
         osx_cross_compile,
         build_type,
         assertions,
-        python_path,
         libcxx_include_dir,
         build_wasm,
         is_final_stage=(stages == 1),
@@ -913,7 +906,6 @@ if __name__ == "__main__":
             osx_cross_compile,
             build_type,
             assertions,
-            python_path,
             libcxx_include_dir,
             build_wasm,
             compiler_rt_source_dir,
@@ -945,7 +937,6 @@ if __name__ == "__main__":
             osx_cross_compile,
             build_type,
             assertions,
-            python_path,
             libcxx_include_dir,
             build_wasm,
             compiler_rt_source_dir,
@@ -986,7 +977,6 @@ if __name__ == "__main__":
             osx_cross_compile,
             build_type,
             assertions,
-            python_path,
             libcxx_include_dir,
             build_wasm,
             compiler_rt_source_dir,