[Huang-404-Q]

Subprocess.__init__ sets terminated_by_signal, but the signal attribute was removed while four XML/JSON output tests still read p.signal on the crash path:

• googletest/test/gtest_xml_output_unittest.py:394
• googletest/test/gtest_xml_output_unittest.py:464
• googletest/test/googletest-json-output-unittest.py:821
• googletest/test/googletest-json-output-unittest.py:870

When a tested binary is killed by a signal, those branches raise AttributeError instead of reporting was killed by signal N, masking the real failure.

Repro (Windows and POSIX both set the high bit):

import sys, gtest_test_utils
p = gtest_test_utils.Subprocess([sys.executable, '-c', 'import os; os.abort()'])
print(p.terminated_by_signal)  # True
print(p.signal)                # AttributeError

Restore the old computation ((~return_code & 0x7fffffff) + 1) and add gtest_test_utils_test.py, which asserts the attribute exists on a signal death. The test is registered in CMake and Bazel.

Verified locally: the new test fails with AttributeError without the fix and passes with it.