CMake: Fold HLSL source into glslang

... and stub the HLSL target.

Fixes the building of shared libraries.

This breaks the cyclic dependency between the `glslang` and `hlsl` targets (by essentially removing the `hlsl` target).

The `BUILD.gn` and `BUILD.bazel` build rules already pull the `HLSL` source into the `glslang` target.

`Android.mk` is the only remaining build config that has a dedicated `HLSL` target, but this is explicity static and does not suffer the same link-time issues with the cyclic dependency (we may wish to stub this target too).

Related issue: #1484, #2147
Related PR: #2267

hlsl/CMakeLists.txt

@@ -1,25 +1,10 @@
-set(SOURCES
-    hlslAttributes.cpp
-    hlslParseHelper.cpp
-    hlslScanContext.cpp
-    hlslOpMap.cpp
-    hlslTokenStream.cpp
-    hlslGrammar.cpp
-    hlslParseables.cpp)
 
-set(HEADERS
-    hlslAttributes.h
-    hlslParseHelper.h
-    hlslTokens.h
-    hlslScanContext.h
-    hlslOpMap.h
-    hlslTokenStream.h
-    hlslGrammar.h
-    hlslParseables.h)
+# The HLSL source is directly embedded into the glslang target when ENABLE_HLSL
+# is set.
+# The HLSL target is now just a stub that exists for backwards compatibility for
+# projects that referenced this target.
 
-glslang_pch(SOURCES pch.cpp)
-
-add_library(HLSL ${LIB_TYPE} ${SOURCES} ${HEADERS})
+add_library(HLSL ${LIB_TYPE} "stub.cpp")
 set_property(TARGET HLSL PROPERTY FOLDER hlsl)
 set_property(TARGET HLSL PROPERTY POSITION_INDEPENDENT_CODE ON)
 
@@ -27,10 +12,6 @@ if(WIN32 AND BUILD_SHARED_LIBS)
     set_target_properties(HLSL PROPERTIES PREFIX "")
 endif()
 
-if(WIN32)
-    source_group("Source" FILES ${SOURCES} ${HEADERS})
-endif(WIN32)
-
 if(ENABLE_GLSLANG_INSTALL)
     if(BUILD_SHARED_LIBS)
         install(TARGETS HLSL EXPORT HLSLTargets