Disable RVV code, fails to build on riscv64.

Index: unac/simdutf.h
--- unac/simdutf.h.orig
+++ unac/simdutf.h
@@ -150,7 +150,7 @@
 #endif
 
 #if __riscv_v_intrinsic >= 11000
-#define SIMDUTF_HAS_RVV_INTRINSICS 1
+#define SIMDUTF_HAS_RVV_INTRINSICS 0
 #endif
 
 #define SIMDUTF_HAS_ZVBB_INTRINSICS 0 // there is currently no way to detect this
