[lit] Export env vars in script to avoid pruning (#105759)

On macOS the dynamic loader prunes dyld specific environment variables
such as `DYLD_INSERT_LIBRARIES`, `DYLD_LIBRARY_PATH`, etc. If these are
set in the lit config it's safe to assume that the user actually wanted
their subprocesses to run with these variables, versus the python
interpreter that gets executed with them before they are pruned. This
change exports all known variables in the shell script instead of
relying on them being passed through.

llvm/utils/lit/lit/TestRunner.py

@@ -1226,6 +1226,16 @@ def executeScript(test, litConfig, tmpBase, commands, cwd):
                     commands[i] += f" && {{ {command}; }}"
         if test.config.pipefail:
             f.write(b"set -o pipefail;" if mode == "wb" else "set -o pipefail;")
+
+        # Manually export any DYLD_* variables used by dyld on macOS because
+        # otherwise they are lost when the shell executable is run, before the
+        # lit test is executed.
+        env_str = "\n".join(
+            "export {}={};".format(k, shlex.quote(v))
+            for k, v in test.config.environment.items()
+            if k.startswith("DYLD_")
+        )
+        f.write(bytes(env_str, "utf-8") if mode == "wb" else env_str)
         f.write(b"set -x;" if mode == "wb" else "set -x;")
         if sys.version_info > (3, 0) and mode == "wb":
             f.write(bytes("{ " + "; } &&\n{ ".join(commands) + "; }", "utf-8"))