CMake dxc as subproject fixes (microsoft#6050)

These changes allow us to use DXC as as CMake subproject (via
add_subdirectory).

Commit comments from each commit:

===

cmake: allow CMAKE_INSTALL_RPATH to be defined in superproject on APPLE
platforms

As on Linux, allow CMAKE_INSTALL_RPATH to be defined in a CMake
superproject.

===

cmake: Allow LLVM_ENABLE_ASSERTIONS=OFF to disable assertions in Debug
builds

Currently, this flag is only used to enable assertions in non-Debug
builds, but is not respected in Debug builds. That is, if set to false,
Debug builds will still assert. This change fixes that.

Note that by default, LLVM_ENABLE_ASSERTIONS is true in Debug builds, so
unless it's explicitly set to false, this is a no-op for most people.

===

cmake: Allow DIRECTX_HEADERS_INCLUDE_DIR to be defined from superproject

Useful for when DXC is included as a subdirectory. In Dawn/Chrome, we
use our own mirror of DirectX-Headers instead of checking out the repo's
submodules, so we need to override this variable.

CMakeLists.txt

@@ -588,8 +588,10 @@ set( CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}
 
 set(CMAKE_BUILD_WITH_INSTALL_RPATH ON)
 if (APPLE)
-  set(CMAKE_INSTALL_NAME_DIR "@rpath")
-  set(CMAKE_INSTALL_RPATH "@executable_path/../lib")
+  if(NOT DEFINED CMAKE_INSTALL_RPATH)
+    set(CMAKE_INSTALL_NAME_DIR "@rpath")
+    set(CMAKE_INSTALL_RPATH "@executable_path/../lib")
+    endif(NOT DEFINED CMAKE_INSTALL_RPATH)
 else(UNIX)
   if(NOT DEFINED CMAKE_INSTALL_RPATH)
     set(CMAKE_INSTALL_RPATH "\$ORIGIN/../lib${LLVM_LIBDIR_SUFFIX}")

cmake/modules/HandleLLVMOptions.cmake

@@ -78,6 +78,11 @@ if( LLVM_ENABLE_ASSERTIONS )
         "${flags_var_to_scrub}" "${${flags_var_to_scrub}}")
     endforeach()
   endif()
+else()
+  # Disable assertions in Debug builds
+  if( uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" )
+    add_definitions( -DNDEBUG )
+  endif()
 endif()
 
 string(TOUPPER "${LLVM_ABI_BREAKING_CHECKS}" uppercase_LLVM_ABI_BREAKING_CHECKS)

external/CMakeLists.txt

@@ -8,13 +8,15 @@ if (NOT HLSL_ENABLE_DEBUG_ITERATORS)
 endif (NOT HLSL_ENABLE_DEBUG_ITERATORS)
 
 # Need DirectX-Headers module if not on windows
-if (NOT WIN32)
-  if (IS_DIRECTORY "${DXC_EXTERNAL_ROOT_DIR}/DirectX-Headers")
-    set(DIRECTX_HEADER_INCLUDE_DIR ${DXC_EXTERNAL_ROOT_DIR}/DirectX-Headers/include PARENT_SCOPE)
-  else()
-    message(FATAL_ERROR "DirectX-Headers was not found - required for reflection support on *nix see https://github.com/microsoft/DirectX-Headers")
-  endif()
-endif (NOT WIN32)
+if (NOT DIRECTX_HEADER_INCLUDE_DIR)
+  if (NOT WIN32)
+    if (IS_DIRECTORY "${DXC_EXTERNAL_ROOT_DIR}/DirectX-Headers")
+      set(DIRECTX_HEADER_INCLUDE_DIR ${DXC_EXTERNAL_ROOT_DIR}/DirectX-Headers/include PARENT_SCOPE)
+    else()
+      message(FATAL_ERROR "DirectX-Headers was not found - required for reflection support on *nix see https://github.com/microsoft/DirectX-Headers")
+    endif()
+  endif (NOT WIN32)
+endif(NOT DIRECTX_HEADER_INCLUDE_DIR)
 
 # Enabling SPIR-V codegen requires SPIRV-Headers for spirv.hpp and
 # SPIRV-Tools for SPIR-V disassembling functionality.