[HLSL] Correctly set __HLSL_ENABLE_16_BIT (llvm#89788)

The preprocessor define `__HLSL_ENABLE_16_BIT` should be set to 1 if
native 16-bit types are enabled and not set if they are not.

Previously we were setting the value to match the HLSL active language
version, and we had no test coverage verifing the value was set and not
set as expected.

Fixes llvm#89787

Author: llvm-beanz

clang/lib/Frontend/InitPreprocessor.cpp

@@ -389,8 +389,7 @@ static void InitializeStandardPredefinedMacros(const TargetInfo &TI,
                         Twine((unsigned)LangOpts.getHLSLVersion()));
 
     if (LangOpts.NativeHalfType)
-      Builder.defineMacro("__HLSL_ENABLE_16_BIT",
-                          Twine((unsigned)LangOpts.getHLSLVersion()));
+      Builder.defineMacro("__HLSL_ENABLE_16_BIT", "1");
 
     // Shader target information
     // "enums" for shader stages

clang/test/Preprocessor/predefined-macros-hlsl.hlsl

@@ -1,14 +1,19 @@
-// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-amplification | FileCheck -match-full-lines %s --check-prefixes=CHECK,AMPLIFICATION
-// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-compute | FileCheck -match-full-lines %s --check-prefixes=CHECK,COMPUTE
-// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-domain | FileCheck -match-full-lines %s --check-prefixes=CHECK,DOMAIN
-// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-geometry | FileCheck -match-full-lines %s --check-prefixes=CHECK,GEOMETRY
-// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-hull | FileCheck -match-full-lines %s --check-prefixes=CHECK,HULL
-// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-library | FileCheck -match-full-lines %s --check-prefixes=CHECK,LIBRARY
-// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-mesh | FileCheck -match-full-lines %s --check-prefixes=CHECK,MESH
-// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-pixel | FileCheck -match-full-lines %s --check-prefixes=CHECK,PIXEL
-// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-vertex | FileCheck -match-full-lines %s --check-prefixes=CHECK,VERTEX
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-amplification | FileCheck -match-full-lines %s --check-prefixes=CHECK,AMPLIFICATION,NOHALF
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-compute | FileCheck -match-full-lines %s --check-prefixes=CHECK,COMPUTE,NOHALF
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-domain | FileCheck -match-full-lines %s --check-prefixes=CHECK,DOMAIN,NOHALF
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-geometry | FileCheck -match-full-lines %s --check-prefixes=CHECK,GEOMETRY,NOHALF
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-hull | FileCheck -match-full-lines %s --check-prefixes=CHECK,HULL,NOHALF
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-library | FileCheck -match-full-lines %s --check-prefixes=CHECK,LIBRARY,NOHALF
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-mesh | FileCheck -match-full-lines %s --check-prefixes=CHECK,MESH,NOHALF
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-pixel | FileCheck -match-full-lines %s --check-prefixes=CHECK,PIXEL,NOHALF
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-vertex | FileCheck -match-full-lines %s --check-prefixes=CHECK,VERTEX,NOHALF
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.3-vertex -fnative-half-type | FileCheck -match-full-lines %s --check-prefixes=CHECK,VERTEX,HALF
+
+// HALF: #define __HLSL_ENABLE_16_BIT 1
+// NOHALF-NOT: __HLSL_ENABLE_16_BIT
 
 // CHECK: #define __HLSL_VERSION 2021
+
 // CHECK: #define __SHADER_STAGE_AMPLIFICATION 14
 // CHECK: #define __SHADER_STAGE_COMPUTE 5
 // CHECK: #define __SHADER_STAGE_DOMAIN 4