Add USE_CLANG_LLD and use_clang_lld.

* USE_CLANG_LLD is unedefined in current builds.
* When USE_CLANG_LLD is defined to 'true' or '1',
  use clang's lld instead of ld or ld.gold.
* When lld is enabled:
  * ld-only flags are not passed to 'lld'.
  * location_packer is disabled.
  * Use new lld's --pack-dyn-relocs=android.
* When lld does not work:
  * In Android.mk files use LOCAL_USE_CLANG_LLD := false.
  * In Android.bp files use use_clang_lld: false.
* Only arm, arm64, x86, and x86_64_devices have LLD flags;
  all other hosts and targets do not call lld yet.

Bug: 73768157
Test: make checkbuild and boot
Change-Id: I06b8a1e868a600997a7e70fe05c299d751d23d5f
diff --git a/cc/config/x86_linux_bionic_host.go b/cc/config/x86_linux_bionic_host.go
index 9f0bbbd..057e905 100644
--- a/cc/config/x86_linux_bionic_host.go
+++ b/cc/config/x86_linux_bionic_host.go
@@ -126,6 +126,11 @@
 	return "${config.LinuxBionicLdflags}"
 }
 
+func (t *toolchainLinuxBionic) ClangLldflags() string {
+	// TODO: define and use LinuxBionicLldflags
+	return "${config.LinuxBionicLdflags}"
+}
+
 func (t *toolchainLinuxBionic) ToolchainClangCflags() string {
 	return "-m64 -march=x86-64" +
 		// TODO: We're not really android, but we don't have a triple yet b/31393676