Add testing infrastructure to check if gdb is available for testing.

[echristo]

SGTM.

[saugustine]

Thanks. Committed as r371120.

libcxx/test/CMakeLists.txt

set(LIBCXX_EXECUTOR "None" CACHE STRING
     "Executor to use when running tests.")
 
 set(AUTO_GEN_COMMENT "## Autogenerated by libcxx configuration.\n# Do not edit!")
 
 if (NOT DEFINED LIBCXX_TEST_DEPS)
   message(FATAL_ERROR "Expected LIBCXX_TEST_DEPS to be defined")
 endif()
 
+find_program(LIBCXX_GDB gdb)
+if (LIBCXX_GDB)
+  set(LIBCXX_GDB "${LIBCXX_GDB}")
+  message(STATUS "gdb found: ${LIBCXX_GDB}")
+else()
+  message(STATUS "gdb not found. Disabling dependent tests.")
+endif()
+
 if (LIBCXX_INCLUDE_TESTS)
   include(AddLLVM) # for configure_lit_site_cfg and add_lit_testsuit
 
   configure_lit_site_cfg(
     ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
     ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg)
 
   add_lit_testsuite(check-cxx
set(capture_dirs
       "${LIBCXX_LIB_CMAKEFILES_DIR}/cxx_objects.dir/"
       "${LIBCXX_LIB_CMAKEFILES_DIR}/cxx.dir/"
       "${LIBCXX_LIB_CMAKEFILES_DIR}/cxx_experimental.dir/"
       "${CMAKE_CURRENT_BINARY_DIR}")
   set(extract_dirs "${LIBCXX_SOURCE_DIR}/include;${LIBCXX_SOURCE_DIR}/src")
   setup_lcov_test_target_coverage("cxx" "${output_dir}" "${capture_dirs}" "${extract_dirs}")
 endif()
 
-
 if (LIBCXX_CONFIGURE_IDE)
   # Create dummy targets for each of the tests in the test suite, this allows
   # IDE's such as CLion to correctly highlight the tests because it knows
   # roughly what include paths/compile flags/macro definitions are needed.
   include_directories(support)
   file(GLOB_RECURSE LIBCXX_TESTS ${CMAKE_CURRENT_SOURCE_DIR}/*.pass.cpp)
   file(GLOB LIBCXX_TEST_HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/support/*)
   file(GLOB_RECURSE LIBCXX_HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/../include/*)

libcxx/test/lit.site.cfg.in

 config.builtins_library         = "@LIBCXX_BUILTINS_LIBRARY@"
 config.has_libatomic            = @LIBCXX_HAS_ATOMIC_LIB@
 config.use_libatomic            = @LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB@
 config.debug_build              = @LIBCXX_DEBUG_BUILD@
 config.libcxxabi_shared         = @LIBCXXABI_ENABLE_SHARED@
 config.cxx_ext_threads          = @LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY@
 config.pstl_src_root            = "@ParallelSTL_SOURCE_DIR@" if @LIBCXX_ENABLE_PARALLEL_ALGORITHMS@ else None
 config.pstl_obj_root            = "@ParallelSTL_BINARY_DIR@" if @LIBCXX_ENABLE_PARALLEL_ALGORITHMS@ else None
+config.libcxx_gdb               = "@LIBCXX_GDB@"
 
 # Let the main config do the real work.
 config.loaded_site_config = True
 lit_config.load_config(config, "@LIBCXX_SOURCE_DIR@/test/lit.cfg")

libcxx/utils/libcxx/test/config.py

def configure_features(self):
         # in 'features.h'.
         macros = self.cxx.dumpMacros(flags=['-include', 'features.h'])
         if isinstance(macros, dict) and '__GLIBC__' in macros:
             maj_v, min_v = (macros['__GLIBC__'], macros['__GLIBC_MINOR__'])
             self.config.available_features.add('glibc')
             self.config.available_features.add('glibc-%s' % maj_v)
             self.config.available_features.add('glibc-%s.%s' % (maj_v, min_v))
 
+        if 'NOTFOUND' not in self.get_lit_conf('libcxx_gdb'):
+            self.config.available_features.add('libcxx_gdb')
+            self.cxx.libcxx_gdb = self.get_lit_conf('libcxx_gdb')
+
         # Support Objective-C++ only on MacOS and if the compiler supports it.
         if self.target_info.platform() == "darwin" and \
            self.target_info.is_host_macosx() and \
            self.cxx.hasCompileFlag(["-x", "objective-c++", "-fobjc-arc"]):
             self.config.available_features.add("objective-c++")
 
     def configure_compile_flags(self):
         self.configure_default_compile_flags()
def configure_substitutions(self):
         sub.append(('%build', build_str))
         # Configure exec prefix substitutions.
         # Configure run env substitution.
         sub.append(('%run', '%t.exe'))
         # Configure not program substitutions
         not_py = os.path.join(self.libcxx_src_root, 'utils', 'not.py')
         not_str = '%s %s ' % (pipes.quote(sys.executable), pipes.quote(not_py))
         sub.append(('not ', not_str))
+        if self.get_lit_conf('libcxx_gdb'):
+            sub.append(('%libcxx_gdb', self.get_lit_conf('libcxx_gdb')))
 
     def can_use_deployment(self):
         # Check if the host is on an Apple platform using clang.
         if not self.target_info.platform() == "darwin":
             return False
         if not self.target_info.is_host_macosx():
             return False
         if not self.cxx.type.endswith('clang'):