Merge #19530: depends: build LTO support into Apple's ld64

5962522 depends: bump native_cctools for fixed lto with external clang (Cory Fields)
00d1ba7 depends: enable lto support for Apple's ld64 (Cory Fields)

Pull request description:

  This didn't work for a few reasons (various toolchain compatibility issues) the last time I tested it, but after the last round of bumps it works with no apparent issues.

  Note that this does not _enable_ LTO by default in any way, only hooks up the machinery for ```-flto``` to work correctly when specified.

  Lines were split for an easier rebase after #17919 is merged.

ACKs for top commit:
  fanquake:
    ACK 5962522. The relevant option upstream is [here](https://github.com/tpoechtrager/cctools-port/blob/master/cctools/m4/llvm.m4#L4).

Tree-SHA512: df2775e74e7bc847e6cef94cb8457d503d6c9e2fdea861e51386fa6ed5a7ba688241db3685561ae1a32f66724c1b3801727252025f00c04b90a3bdc8a4f6f93b

Author: fanquake

depends/packages/native_cctools.mk

@@ -1,8 +1,8 @@
 package=native_cctools
-$(package)_version=4da2f3b485bcf4cef526f30c0b8c0bcda99cdbb4
+$(package)_version=55562e4073dea0fbfd0b20e0bf69ffe6390c7f97
 $(package)_download_path=https://github.com/tpoechtrager/cctools-port/archive
 $(package)_file_name=$($(package)_version).tar.gz
-$(package)_sha256_hash=a2d491c0981cef72fee2b833598f20f42a6c44a7614a61c439bda93d56446fec
+$(package)_sha256_hash=e51995a843533a3dac155dd0c71362dd471597a2d23f13dff194c6285362f875
 $(package)_build_subdir=cctools
 ifeq ($(strip $(FORCE_USE_SYSTEM_CLANG)),)
 $(package)_clang_version=8.0.0
@@ -63,9 +63,10 @@ endef
 endif
 
 define $(package)_set_vars
-  $(package)_config_opts=--target=$(host) --disable-lto-support --with-libtapi=$($(package)_extract_dir)
+  $(package)_config_opts=--target=$(host) --with-libtapi=$($(package)_extract_dir)
   $(package)_ldflags+=-Wl,-rpath=\\$$$$$$$$\$$$$$$$$ORIGIN/../lib
   ifeq ($(strip $(FORCE_USE_SYSTEM_CLANG)),)
+  $(package)_config_opts+=--enable-lto-support --with-llvm-config=$($(package)_extract_dir)/toolchain/bin/llvm-config
   $(package)_cc=$($(package)_extract_dir)/toolchain/bin/clang
   $(package)_cxx=$($(package)_extract_dir)/toolchain/bin/clang++
   else