[compiler-rt] [test] Fix NameError when loading lit.cfg.py for crt

Summary:
The `execute_external` global variable is defined in [`lit.common.cfg.py`](fcfb3170a7/compiler-rt/test/lit.common.cfg.py (L18-L27)) and used here (on lines 23 and 39). However, this variable is not visible in configs that are loaded independently.

Explicitly assign it to the correct value to avoid `NameError`.

Reviewers: compnerd, phosek

Reviewed By: compnerd, phosek

Subscribers: dberris, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D79892

compiler-rt/test/crt/lit.cfg.py

@@ -10,6 +10,17 @@ config.name = 'CRT' + config.name_suffix
 config.test_source_root = os.path.dirname(__file__)
 
 
+# Choose between lit's internal shell pipeline runner and a real shell.  If
+# LIT_USE_INTERNAL_SHELL is in the environment, we use that as an override.
+use_lit_shell = os.environ.get("LIT_USE_INTERNAL_SHELL")
+if use_lit_shell:
+    # 0 is external, "" is default, and everything else is internal.
+    execute_external = (use_lit_shell == "0")
+else:
+    # Otherwise we default to internal on Windows and external elsewhere, as
+    # bash on Windows is usually very slow.
+    execute_external = (not sys.platform in ['win32'])
+
 def get_library_path(file):
     cmd = subprocess.Popen([config.clang.strip(),
                             config.target_cflags.strip(),