Fix verilog_treebuilder_utils_test on Windows

[corco]

The WrongClose test was failing on Windows with

external/com_google_googletest/googletest/src/gtest-port.cc(865): error: Failed
Syntax error at index 0 in simple regular expression "}": '}' is unsupported.
Stack trace:
  00007FF780051A8F: testing::internal::RE::Init
  00007FF78002BC9F: testing::internal::RE::RE
  00007FF78002BAAC: testing::ContainsRegex<const char *>
  00007FF78002B72C: testing::internal::MakeDeathTestMatcher
  00007FF780023CF7: verilog::`anonymous namespace'::MakeParenGroupTest_WrongClose_Test::TestBody
  00007FF78009B000: testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test,void>
  00007FF780085E3F: testing::internal::HandleExceptionsInMethodIfSupported<testing::Test,void>
  00007FF78006C8B9: testing::Test::Run
  00007FF78006D58C: testing::TestInfo::Run
  00007FF78006DF09: testing::TestSuite::Run
... Google Test internal frames ...

Running main() from gmock_main.cc
verilog/CST/verilog_treebuilder_utils_test.cc(55): error: Death test: MakeParenGroup(Leaf('(', "("), Leaf(1, "1"), Leaf('}', "}"))
    Result: died but not with expected error.
  Expected: contains regular expression "}"

Escaping the } fixes the issue. Note that this error is the same as if line 50 is not escaped. I could not figure out why the test passed on Linux, but now it passes on every platform.

[hzeller]

Interesting find!
Thanks, merged.