Remove 'abi-breaking-checks' lit feature.

[thakis]

Summary

Its only two uses were removed in r311730.

Effectively reverts r304851 (but that code has removed around a bit since then).

[mgrang]

LGTM. r311730 was initially based on ABI_BREAKING_CHECKS but according to review comments, it seemed better w/o that check. So abi-breaking ended up being never used. I think we can safely remove this.

[thakis]

r331872, thanks!

test/lit.site.cfg.py.in

 config.ocamlfind_executable = "@OCAMLFIND@"
 config.have_ocamlopt = @HAVE_OCAMLOPT@
 config.have_ocaml_ounit = @HAVE_OCAML_OUNIT@
 config.ocaml_flags = "@OCAMLFLAGS@"
 config.include_go_tests = @LLVM_INCLUDE_GO_TESTS@
 config.go_executable = "@GO_EXECUTABLE@"
 config.enable_shared = @ENABLE_SHARED@
 config.enable_assertions = @ENABLE_ASSERTIONS@
-config.enable_abi_breaking_checks = "@LLVM_ENABLE_ABI_BREAKING_CHECKS@"
 config.targets_to_build = "@TARGETS_TO_BUILD@"
 config.native_target = "@LLVM_NATIVE_ARCH@"
 config.llvm_bindings = "@LLVM_BINDINGS@".split(' ')
 config.host_os = "@HOST_OS@"
 config.host_cc = "@HOST_CC@"
 config.host_cxx = "@HOST_CXX@"
 config.host_ldflags = "@HOST_LDFLAGS@"
 config.llvm_use_intel_jitevents = @LLVM_USE_INTEL_JITEVENTS@

utils/lit/lit/llvm/config.py

def __init__(self, lit_config, config):
             # Allow use of an explicit path for gmalloc library.
             # Will default to '/usr/lib/libgmalloc.dylib' if not set.
             gmalloc_path_str = lit_config.params.get('gmalloc_path',
                                                      '/usr/lib/libgmalloc.dylib')
             if gmalloc_path_str is not None:
                 self.with_environment(
                     'DYLD_INSERT_LIBRARIES', gmalloc_path_str)
 
-        breaking_checks = getattr(config, 'enable_abi_breaking_checks', None)
-        if lit.util.pythonize_bool(breaking_checks):
-            features.add('abi-breaking-checks')
-
     def with_environment(self, variable, value, append_path=False):
         if append_path:
             # For paths, we should be able to take a list of them and process all
             # of them.
             paths_to_add = value
             if lit.util.is_string(paths_to_add):
                 paths_to_add = [paths_to_add]