Make 'use_clang_lld' property specifiable per architecture

Bug: http://b/73768157

Test: Mark 'use_clang_lld: true' for one arch of a module and verify by
inspection that only that arch variant uses lld.

Change-Id: I4b0d7a2bc43ee0b8462ab09a5f5c50807129a7fb

cc/linker.go

@@ -59,7 +59,7 @@ type BaseLinkerProperties struct {
 	No_libgcc *bool
 
 	// Use clang lld instead of gnu ld.
-	Use_clang_lld *bool
+	Use_clang_lld *bool `android:"arch_variant"`
 
 	// -l arguments to pass to linker for host-provided shared libraries
 	Host_ldlibs []string `android:"arch_variant"`