Fix no-enum-constexpr-conversion compilation error in DX12 backend with clang-cl (#696)

The warning suppression -Wno-enum-constexpr-conversion no longer works
on recent Clang versions because the warning it used to suppress has been
promoted to an error that cannot be disabled
(see llvm/llvm-project#59036).

Also, the previous error in RootParamsManager.cpp was due to converting -1
to a D3D12_DESCRIPTOR_RANGE_TYPE enum in a constexpr context. Clang rejects
this, but it allows the conversion for a regular const. The code has been
updated to use a const instead of constexpr, making the conversion valid.

Since the original issue that motivated the warning suppression no longer
applies, we can safely remove -Wno-enum-constexpr-conversion.

Co-authored-by: Assiduous <[email protected]>

Author: JKot-Coder

CMakeLists.txt

@@ -486,7 +486,6 @@ if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
         INTERFACE
             -Wno-microsoft-exception-spec
             -Wno-tautological-constant-out-of-range-compare
-            -Wno-enum-constexpr-conversion
         )
     elseif (PLATFORM_APPLE)
         # Allow unavailable API warnings not being errors as they tend to randomly

Graphics/GraphicsEngineD3D12/src/RootParamsManager.cpp

@@ -39,7 +39,7 @@ namespace Diligent
 namespace
 {
 
-constexpr D3D12_DESCRIPTOR_RANGE_TYPE InvalidDescriptorRangeType = static_cast<D3D12_DESCRIPTOR_RANGE_TYPE>(-1);
+const D3D12_DESCRIPTOR_RANGE_TYPE InvalidDescriptorRangeType = static_cast<D3D12_DESCRIPTOR_RANGE_TYPE>(-1);
 
 #ifdef DILIGENT_DEBUG
 void DbgValidateD3D12RootTable(const D3D12_ROOT_DESCRIPTOR_TABLE& d3d12Tbl)