[libc] Add support for sqrt in riscv

[sivachandra]

OK from me but wait for @lntue . Also, include information on what would change functionally or qualitatively with this change.

libc/src/__support/FPUtil/riscv64/sqrt.h

+//===-- Square root of IEEE 754 floating point numbers ----------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SUPPORT_FPUTIL_RISCV64_SQRT_H
+#define LLVM_LIBC_SRC_SUPPORT_FPUTIL_RISCV64_SQRT_H
+
+#include "src/__support/common.h"
+#include "src/__support/macros/properties/architectures.h"
+
+#if !defined(LIBC_TARGET_ARCH_IS_RISCV64)
+#error "Invalid include"
+#endif
+
+#include "src/__support/FPUtil/generic/sqrt.h"
+
+namespace __llvm_libc {
+namespace fputil {
+
+template <> LIBC_INLINE float sqrt<float>(float x) {
+  float result;
+  __asm__ __volatile__("fsqrt.s %0, %1\n\t" : "=f"(result) : "f"(x));
+  return result;
+}
+
+template <> LIBC_INLINE double sqrt<double>(double x) {
+  double result;
+  __asm__ __volatile__("fsqrt.d %0, %1\n\t" : "=f"(result) : "f"(x));
+  return result;
+}
+
+} // namespace fputil
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SUPPORT_FPUTIL_RISCV64_SQRT_H

libc/src/__support/FPUtil/sqrt.h

 #define LLVM_LIBC_SRC_SUPPORT_FPUTIL_SQRT_H
 
 #include "src/__support/macros/properties/architectures.h"
 
 #if defined(LIBC_TARGET_ARCH_IS_X86_64)
 #include "x86_64/sqrt.h"
 #elif defined(LIBC_TARGET_ARCH_IS_AARCH64)
 #include "aarch64/sqrt.h"
+#elif defined(LIBC_TARGET_ARCH_IS_RISCV64)
+#include "riscv64/sqrt.h"
 #else
 #include "generic/sqrt.h"
 
 #endif
 #endif // LLVM_LIBC_SRC_SUPPORT_FPUTIL_SQRT_H