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/linker.go b/cc/linker.go
index bcedc8d..2176306 100644
--- a/cc/linker.go
+++ b/cc/linker.go
@@ -58,6 +58,9 @@
 	// don't link in libgcc.a
 	No_libgcc *bool
 
+	// Use clang lld instead of gnu ld.
+	Use_clang_lld *bool
+
 	// -l arguments to pass to linker for host-provided shared libraries
 	Host_ldlibs []string `android:"arch_variant"`
 
@@ -201,6 +204,15 @@
 	return deps
 }
 
+func (linker *baseLinker) useClangLld(ctx ModuleContext) bool {
+	if linker.Properties.Use_clang_lld != nil {
+		return Bool(linker.Properties.Use_clang_lld)
+	}
+	return ctx.Config().UseClangLld()
+}
+
+// ModuleContext extends BaseModuleContext
+// BaseModuleContext should know if LLD is used?
 func (linker *baseLinker) linkerFlags(ctx ModuleContext, flags Flags) Flags {
 	toolchain := ctx.toolchain()
 
@@ -209,7 +221,11 @@
 		hod = "Device"
 	}
 
-	flags.LdFlags = append(flags.LdFlags, fmt.Sprintf("${config.%sGlobalLdflags}", hod))
+	if flags.Clang && linker.useClangLld(ctx) {
+		flags.LdFlags = append(flags.LdFlags, fmt.Sprintf("${config.%sGlobalLldflags}", hod))
+	} else {
+		flags.LdFlags = append(flags.LdFlags, fmt.Sprintf("${config.%sGlobalLdflags}", hod))
+	}
 	if Bool(linker.Properties.Allow_undefined_symbols) {
 		if ctx.Darwin() {
 			// darwin defaults to treating undefined symbols as errors
@@ -219,7 +235,9 @@
 		flags.LdFlags = append(flags.LdFlags, "-Wl,--no-undefined")
 	}
 
-	if flags.Clang {
+	if flags.Clang && linker.useClangLld(ctx) {
+		flags.LdFlags = append(flags.LdFlags, toolchain.ClangLldflags())
+	} else if flags.Clang {
 		flags.LdFlags = append(flags.LdFlags, toolchain.ClangLdflags())
 	} else {
 		flags.LdFlags = append(flags.LdFlags, toolchain.Ldflags())