string/memory functions: avoid qemu bugs/performance issues.

Use V on real hardware, but GC on qemu.

Change-Id: I419546d94555540e14a14dcc52bd99413cbbcfa1
diff --git a/libc/arch-riscv64/string/memmove.c b/libc/arch-riscv64/string/memmove.c
new file mode 100644
index 0000000..e9bb2c2
--- /dev/null
+++ b/libc/arch-riscv64/string/memmove.c
@@ -0,0 +1,2 @@
+#define	MEMMOVE
+#include "bcopy.c"