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/arm_device.go b/cc/config/arm_device.go
index 66b3b38..02bd9eb 100644
--- a/cc/config/arm_device.go
+++ b/cc/config/arm_device.go
@@ -39,6 +39,8 @@
 		"-Wl,-m,armelf",
 	}
 
+	armLldflags = ClangFilterUnknownLldflags(armLdflags)
+
 	armArmCflags = []string{
 		"-fstrict-aliasing",
 	}
@@ -169,6 +171,7 @@
 	pctx.StaticVariable("ArmToolchainCflags", strings.Join(armToolchainCflags, " "))
 	pctx.StaticVariable("ArmCflags", strings.Join(armCflags, " "))
 	pctx.StaticVariable("ArmLdflags", strings.Join(armLdflags, " "))
+	pctx.StaticVariable("ArmLldflags", strings.Join(armLldflags, " "))
 	pctx.StaticVariable("ArmCppflags", strings.Join(armCppflags, " "))
 	pctx.StaticVariable("ArmIncludeFlags", bionicHeaders("arm"))
 
@@ -196,6 +199,7 @@
 	pctx.StaticVariable("ArmToolchainClangCflags", strings.Join(ClangFilterUnknownCflags(armToolchainCflags), " "))
 	pctx.StaticVariable("ArmClangCflags", strings.Join(ClangFilterUnknownCflags(armCflags), " "))
 	pctx.StaticVariable("ArmClangLdflags", strings.Join(ClangFilterUnknownCflags(armLdflags), " "))
+	pctx.StaticVariable("ArmClangLldflags", strings.Join(ClangFilterUnknownCflags(armLldflags), " "))
 	pctx.StaticVariable("ArmClangCppflags", strings.Join(ClangFilterUnknownCflags(armCppflags), " "))
 
 	// Clang ARM vs. Thumb instruction set cflags
@@ -274,6 +278,7 @@
 type toolchainArm struct {
 	toolchain32Bit
 	ldflags                               string
+	lldflags                              string
 	toolchainCflags, toolchainClangCflags string
 }
 
@@ -350,6 +355,10 @@
 	return t.ldflags
 }
 
+func (t *toolchainArm) ClangLldflags() string {
+	return t.lldflags // TODO: handle V8 cases
+}
+
 func (t *toolchainArm) ClangInstructionSetFlags(isa string) (string, error) {
 	switch isa {
 	case "arm":
@@ -403,6 +412,7 @@
 			"${config.ArmLdflags}",
 			fixCortexA8,
 		}, " "),
+		lldflags:             "${config.ArmLldflags}",
 		toolchainClangCflags: strings.Join(toolchainClangCflags, " "),
 	}
 }