[libcxx] Fix exception raised during downstream bare-metal libunwind tests

[amilendra]

Summary

Fix for the following exception.

AttributeError: 'TestingConfig' object has no attribute 'target_triple'

Related revision: https://reviews.llvm.org/D102012

'TestingConfig' object has no attribute 'target_triple'

[amilendra]

Ping?

[miyuki]

This looks sensible, given that libcxxabi/test/libcxxabi/test/config.py does the same thing:

74         triple = self.get_lit_conf('target_triple', None)
75         if triple is not None:

[miyuki]

Ping^2

[danielkiss]

LGTM

[mstorsjo]

LGTM

libunwind/test/libunwind/test/config.py

def configure_features(self):
             self.config.available_features.add('libunwind-arm-ehabi')
 
     def configure_compile_flags(self):
         self.cxx.compile_flags += ['-DLIBUNWIND_NO_TIMER']
         # Stack unwinding tests need unwinding tables and these are not
         # generated by default on all Targets.
         self.cxx.compile_flags += ['-funwind-tables']
         # Make symbols available in the tests.
-        if 'linux' in self.config.target_triple:
+        triple = self.get_lit_conf('target_triple', None)
+        if 'linux' in triple:
             self.cxx.link_flags += ['-Wl,--export-dynamic']
         if not self.get_lit_bool('enable_threads', True):
             self.cxx.compile_flags += ['-D_LIBUNWIND_HAS_NO_THREADS']
             self.config.available_features.add('libunwind-no-threads')
         super(Configuration, self).configure_compile_flags()
 
     def configure_compile_flags_header_includes(self):
         libunwind_headers = self.get_lit_conf(