Implement rvv version mem* and str* for riscv64

Add vector version mem* and str* functions and only build them when the
vector extension is enabled.
The original implementation comes from
https://github.com/sifive/sifive-libc, which we agree to contribute to
the Android Open Source Project.

Test: mma

Change-Id: I11b671a5bc571d7c783a657f272f282df7d16c29
Signed-off-by: Yun Hsiang <yun.hsiang@sifive.com>
diff --git a/libc/arch-riscv64/dynamic_function_dispatch.cpp b/libc/arch-riscv64/dynamic_function_dispatch.cpp
new file mode 100644
index 0000000..0925c5f
--- /dev/null
+++ b/libc/arch-riscv64/dynamic_function_dispatch.cpp
@@ -0,0 +1,107 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <private/bionic_ifuncs.h>
+#include <stddef.h>
+#include <sys/auxv.h>
+
+#if defined(__riscv_v)
+extern "C" {
+
+typedef void* memchr_func(const void*, int, size_t);
+DEFINE_IFUNC_FOR(memchr) {
+  RETURN_FUNC(memchr_func, memchr_vext);
+}
+
+typedef int memcmp_func(const void*, const void*, size_t);
+DEFINE_IFUNC_FOR(memcmp) {
+  RETURN_FUNC(memcmp_func, memcmp_vext);
+}
+
+typedef void* memcpy_func(void*, const void*, size_t);
+DEFINE_IFUNC_FOR(memcpy) {
+  RETURN_FUNC(memcpy_func, memcpy_vext);
+}
+
+typedef void* memmove_func(void*, const void*, size_t);
+DEFINE_IFUNC_FOR(memmove) {
+  RETURN_FUNC(memmove_func, memmove_vext);
+}
+
+typedef void* memset_func(void*, int, size_t);
+DEFINE_IFUNC_FOR(memset) {
+  RETURN_FUNC(memset_func, memset_vext);
+}
+
+typedef char* strcat_func(char*, const char*);
+DEFINE_IFUNC_FOR(strcat) {
+  RETURN_FUNC(strcat_func, strcat_vext);
+}
+
+typedef char* strchr_func(const char*, int);
+DEFINE_IFUNC_FOR(strchr) {
+  RETURN_FUNC(strchr_func, strchr_vext);
+}
+
+typedef int strcmp_func(const char*, const char*);
+DEFINE_IFUNC_FOR(strcmp) {
+  RETURN_FUNC(strcmp_func, strcmp_vext);
+}
+
+typedef char* strcpy_func(char*, const char*);
+DEFINE_IFUNC_FOR(strcpy) {
+  RETURN_FUNC(strcpy_func, strcpy_vext);
+}
+
+typedef size_t strlen_func(const char*);
+DEFINE_IFUNC_FOR(strlen) {
+  RETURN_FUNC(strlen_func, strlen_vext);
+}
+
+typedef char* strncat_func(char*, const char*, size_t);
+DEFINE_IFUNC_FOR(strncat) {
+  RETURN_FUNC(strncat_func, strncat_vext);
+}
+
+typedef int strncmp_func(const char*, const char*, size_t);
+DEFINE_IFUNC_FOR(strncmp) {
+  RETURN_FUNC(strncmp_func, strncmp_vext);
+}
+
+typedef char* strncpy_func(char*, const char*, size_t);
+DEFINE_IFUNC_FOR(strncpy) {
+  RETURN_FUNC(strncpy_func, strncpy_vext);
+}
+
+typedef size_t strnlen_func(const char*, size_t);
+DEFINE_IFUNC_FOR(strnlen) {
+  RETURN_FUNC(strnlen_func, strnlen_vext);
+}
+
+}  // extern "C"
+#endif