[HLSL] add asin library function

[bob80905]

Summary

This change exposes the asin library function for HLSL scalar types,
excluding long long doubles. Asin is supported for all scalar, vector,
and matrix types. This patch only adds a subset of scalar type support.

Long long double support is missing in this patch because that type
doesn't exist in HLSL.

The full documentation of the HLSL asin function is available here:
https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-asin

clang/lib/Headers/hlsl/hlsl_intrinsics.h

 //===----- hlsl_intrinsics.h - HLSL definitions for intrinsics ----------===//
 //
 // 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 _HLSL_HLSL_INTRINSICS_H_
 #define _HLSL_HLSL_INTRINSICS_H_
 
 __attribute__((clang_builtin_alias(__builtin_hlsl_wave_active_count_bits))) uint
 WaveActiveCountBits(bool bBit);
 
+
+__attribute__((clang_builtin_alias(__builtin_asin))) double asin(double In);
+__attribute__((clang_builtin_alias(__builtin_asinf))) float asin(float In);
+
+
 #endif //_HLSL_HLSL_INTRINSICS_H_

clang/test/CodeGenHLSL/builtins/asin.hlsl

+// RUN: %clang_cc1 -std=hlsl2021 -finclude-default-header -x hlsl -triple \
+// RUN:   dxil-pc-shadermodel6.3-library %s -emit-llvm -disable-llvm-passes \
+// RUN:   -o - | FileCheck %s
+
+double asin_d(double x)
+{
+  return asin(x);
+}
+
+// CHECK: define noundef double @"?asin_d@@YANN@Z"(
+// CHECK: call noundef double @asin(double noundef %0) #2
+
+float asin_f(float x)
+{
+  return asin(x);
+}
+
+// CHECK: define noundef float @"?asin_f@@YAMM@Z"(
+// CHECK: call noundef float @asinf(float noundef %0)