FIX: Clang and MSVC compile options duplicate for clang-cl

[JKot-Coder]

Summary

When building with clang-cl (Clang frontend for MSVC):

• Previously, both Clang-specific and MSVC-specific compiler flags were
  applied, producing duplicate warnings and huge warning output.
• Compilation could slow down by orders of magnitude due to -Wall/-Wextra.

Changes

• Clang-cl now only uses MSVC-specific compile options.
• Pure Clang builds continue using Clang-specific warnings and suppressions.
• Redundant -Wall/-Wextra removed for clang-cl.

Benefits

• Builds with clang-cl are significantly faster.
• Warning output is reasonable and manageable.
• Maintains correct compile flags for each compiler.

[TheMostDiligent]

There are a few other places where clang-specific compiler options are set e.g.
Should they also be disabled for clang-cl?

DiligentCore/Graphics/ShaderTools/CMakeLists.txt

Lines 141 to 143 in c4a98bd

	if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
	target_compile_options(Diligent-ShaderTools PRIVATE -fms-extensions)
	endif()

DiligentCore/Graphics/ShaderTools/CMakeLists.txt

Lines 146 to 149 in c4a98bd

	if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR
	CMAKE_CXX_COMPILER_ID MATCHES "GNU")
	target_link_libraries(Diligent-ShaderTools PRIVATE dl)
	endif()

DiligentCore/Graphics/GraphicsEngineOpenGL/CMakeLists.txt

Lines 223 to 248 in c4a98bd

	if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
	# WARNING: set_source_files_properties() does not append
	# properties, but overwrites them!
	# Disable warnings like this one:
	# comparison of function 'glPolygonMode' not equal to a null pointer is always true [-Wtautological-pointer-compare]
	set_property(SOURCE
	src/RenderDeviceGLImpl.cpp
	src/GLContextState.cpp
	src/DeviceContextGLImpl.cpp
	APPEND_STRING PROPERTY
	COMPILE_FLAGS " -Wno-tautological-pointer-compare"
	)
	if (PLATFORM_IOS)
	# Disable warnings like this one:
	# unused variable 'BottomLeftY' [-Wunused-variable]
	set_property(SOURCE
	src/DeviceContextGLImpl.cpp
	src/GLContextState.cpp
	src/RenderDeviceGLImpl.cpp
	src/Texture1D_GL.cpp
	APPEND_STRING PROPERTY
	COMPILE_FLAGS " -Wno-unused-variable"
	)
	endif()
	endif()

DiligentCore/Tests/DiligentCoreTest/CMakeLists.txt

Lines 25 to 32 in c4a98bd

	if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
	# Disable the following warning:
	# explicitly moving variable of type '(anonymous namespace)::SmartPtr' (aka 'RefCntAutoPtr<(anonymous namespace)::Object>') to itself [-Wself-move]
	set_source_files_properties(src/Common/RefCntAutoPtrTest.cpp
	PROPERTIES
	COMPILE_FLAGS "-Wno-self-move -Wno-self-assign"
	)
	endif()

DiligentCore/Tests/GPUTestFramework/CMakeLists.txt

Lines 126 to 141 in c4a98bd

	if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
	# Disable the following warning:
	# comparison of function 'glPolygonMode' not equal to a null pointer is always true [-Wtautological-pointer-compare]
	set_property(SOURCE
	src/GL/TestingEnvironmentGL.cpp
	APPEND_STRING PROPERTY
	COMPILE_FLAGS -Wno-tautological-pointer-compare
	)
	if (PLATFORM_WEB)
	set_property(SOURCE
	src/GPUTestingEnvironment.cpp
	APPEND_STRING PROPERTY
	COMPILE_FLAGS "-Wno-unused-variable"
	)
	endif()
	endif()

DiligentCore/Tests/DiligentCoreAPITest/CMakeLists.txt

Lines 128 to 141 in c4a98bd

	if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
	# Disable warnings like this one:
	# comparison of function 'glPolygonMode' not equal to a null pointer is always true [-Wtautological-pointer-compare]
	set_source_files_properties(
	src/GL/DrawCommandReferenceGL.cpp
	src/GL/GeometryShaderReferenceGL.cpp
	src/GL/TessellationReferenceGL.cpp
	PROPERTIES
	COMPILE_FLAGS -Wno-tautological-pointer-compare
	)
	if (PLATFORM_WEB)
	set_property(SOURCE ${C_INTERFACE_SOURCE} APPEND_STRING PROPERTY COMPILE_FLAGS "-Wno-unknown-warning-option -Wno-unused-but-set-variable")
	endif()
	endif()

[JKot-Coder]

I'm 99% sure they all should be fixed same way. But I didn't checked any of this.
I'm just started use Diligent and faced with issued that clang++ fails to link at windows.
clang-cl - fails to compile 😄 So I'm just fixed most critical one issues for me. I'm use complied only core and dx12 for now.

[TheMostDiligent]

Did you figure out how to make the build faster?
Last time I tried clang-cl, it took almost 1.5 hours to build everything.

[TheMostDiligent]

This change does not seem to be correct.
If clang-cl only takes MSVC-like command line arguments, the entire branch should be disabled:

if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT MSVC)

This reduces the number of warnings, but build time is still ridiculous. It takes more than 5 minutes to build only Diligent-GraphicsEngineD3D11-static

[JKot-Coder]

if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT MSVC)
Yes, that makes sense.

With all errors ignored using -w, the build completed in less than a minute. Warnings significantly affect build performance.

[TheMostDiligent]

For me, it feels like linking takes most of the time.
Which generator do you use? VS or Ninja?