Implement the `Barrier` HLSL Function

[ ] Implement Barrier clang builtin,
[ ] Link Barrier clang builtin with hlsl_intrinsics.h
[ ] Add sema checks for Barrier to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
[ ] Add codegen for Barrier to EmitHLSLBuiltinExpr in CGBuiltin.cpp
[ ] Add codegen tests to clang/test/CodeGenHLSL/builtins/Barrier.hlsl
[ ] Add sema tests to clang/test/SemaHLSL/BuiltIns/Barrier-errors.hlsl
[ ] Create the int_dx_Barrier intrinsic in IntrinsicsDirectX.td
[ ] Create the DXILOpMapping of int_dx_Barrier to 244 in DXIL.td
[ ] Create the Barrier.ll and Barrier_errors.ll tests in llvm/test/CodeGen/DirectX/

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
244	BarrierByMemoryType	6.8	()

There is no support for Barrier when targeting SPIR-V.

//dxc Barrier_test.hlsl -T lib_6_8 -enable-16bit-types -O0

export void fn() {
    uint p1 = 1;
    uint p2 = 1;

    return Barrier(p1, p2);
}

//dxc Barrier_1_test.hlsl -T lib_6_8 -enable-16bit-types -O0

export void fn() {
    uint p1 = 1;
    uint p2 = 1;

    return Barrier(p1, p2);
}

void Barrier(uint MemoryTypeFlags, uint SemanticFlags);

void Barrier(NodeRecordOrUAV o, uint SemanticFlags);

Name	Template Type	Component Type	Size
ret	void	void	0
MemoryTypeFlags	scalar	uint	1
SemanticFlags	scalar	uint	1

Name	Template Type	Component Type	Size
ret	void	void	0
o	scalar		1
SemanticFlags	scalar	uint	1

This function is supported in the following shader models.	Shader Model	Supported
Shader Model 6.8 and higher shader models	yes