mac: Correctly disable tools/lto tests when building with LLVM_ENABLE_PIC=OFF

[thakis]

Summary

llvm/tools sets LLVM_TOOL_LTO_BUILD to Off if LLVM_ENABLE_PIC=OFF, but that's not visible in llvm/test.

r289662 added the llvm_tool_lto_build lit parameter, there the intent was to use it with an explicit -DLLVM_TOOL_LTO_BUILD=OFF, which is visible globally. On the review for that (D27739), a mild preference was expressed for using a lit parameter over checking the existence of libLTO.dylib. Since that works with the LLVM_ENABLE_PIC=OFF case too and since it matches what we do for the gold plugin, switch to that approach.

[thakis]

mehdi, is this fine with you?

[steven_wu]

Not sure about gn part and if that has any impact. Otherwise, LGTM.

test/lit.cfg.py

def have_ld_plugin_support():
     return True
 
 
 if have_ld_plugin_support():
     config.available_features.add('ld_plugin')
 
 
 def have_ld64_plugin_support():
-    if not config.llvm_tool_lto_build or config.ld64_executable == '':
+    if not os.path.exists(os.path.join(config.llvm_shlib_dir, 'libLTO' + config.llvm_shlib_ext)):
+        return False
+
+    if config.ld64_executable == '':
         return False
 
     ld_cmd = subprocess.Popen(
         [config.ld64_executable, '-v'], stderr=subprocess.PIPE)
     ld_out = ld_cmd.stderr.read().decode()
     ld_cmd.wait()
 
     if 'ld64' not in ld_out or 'LTO' not in ld_out:

test/lit.site.cfg.py.in

 config.llvm_lib_dir = "@LLVM_LIBRARY_DIR@"
 config.llvm_shlib_dir = "@SHLIBDIR@"
 config.llvm_shlib_ext = "@SHLIBEXT@"
 config.llvm_exe_ext = "@EXEEXT@"
 config.lit_tools_dir = "@LLVM_LIT_TOOLS_DIR@"
 config.python_executable = "@PYTHON_EXECUTABLE@"
 config.gold_executable = "@GOLD_EXECUTABLE@"
 config.ld64_executable = "@LD64_EXECUTABLE@"
-config.llvm_tool_lto_build = @LLVM_TOOL_LTO_BUILD@
 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@

utils/gn/secondary/llvm/test/BUILD.gn

extra_values = [
 
     "LLVM_ENABLE_FFI=0",
     "LLVM_HAVE_OPT_VIEWER_MODULES=0",
     "LLVM_HOST_TRIPLE=$llvm_host_triple",
     "LLVM_LIBRARY_DIR=" + rebase_path("$root_out_dir/lib"),
     "LLVM_LINK_LLVM_DYLIB=0",
     "LLVM_LIT_TOOLS_DIR=",  # Intentionally empty, matches cmake build.
     "LLVM_NATIVE_ARCH=$native_target",
-    "LLVM_TOOL_LTO_BUILD=1",  # The GN build always builds //llvm/tools/lto.
     "LLVM_USE_INTEL_JITEVENTS=0",
     "LLVM_USE_SANITIZER=",
     "PYTHON_EXECUTABLE=$python_path",
     "TARGETS_TO_BUILD=$llvm_targets_to_build_string",
     "TARGET_TRIPLE=$llvm_target_triple",
 
     # No bindings are implemented in the GN build.
     "LLVM_BINDINGS=",