Set -fno-emulated-tls for riscv64

Building for riscv64 fails with link errors on __thread variables.
Set -fno-emulated-tls to fix it.

Bug: 254713216
Test: lunch aosp_riscv64-userdebug && m ALLOW_MISSING_DEPENDENCIES=true ndk_sysroot
Change-Id: I3dca81dfd277d681b6c868a5e8385e3a37335a5f
diff --git a/cc/sanitize.go b/cc/sanitize.go
index d39b0eb..b8cc432 100644
--- a/cc/sanitize.go
+++ b/cc/sanitize.go
@@ -511,7 +511,7 @@
 		s.Integer_overflow = nil
 	}
 
-	// CFI doesn't work for riscv64 yet because LTO doesn't work.
+	// TODO(b/254713216): CFI doesn't work for riscv64 yet because LTO doesn't work.
 	if ctx.Arch().ArchType == android.Riscv64 {
 		s.Cfi = nil
 		s.Diag.Cfi = nil