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/config/riscv64_device.go b/cc/config/riscv64_device.go
index d8918f1..825be7f 100644
--- a/cc/config/riscv64_device.go
+++ b/cc/config/riscv64_device.go
@@ -25,6 +25,7 @@
 	riscv64Cflags = []string{
 		// Help catch common 32/64-bit errors.
 		"-Werror=implicit-function-declaration",
+		"-fno-emulated-tls",
 	}
 
 	riscv64ArchVariantCflags = map[string][]string{}