[CMake] Followup for r337366: Only export LLVM_LINK_LLVM_DYLIB it it's set to ON

[philip.pfaffe]

Summary

As it was, always exporting LLVM_LINK_LLVM_DYLIB caused out-of-tree
clients to lose the ability to link against the dylib, even if in-tree tools did
not. By only exporting the setting if it is enabled, out-of-tree clients get the
correct default, but may still choose if they can.

[philip.pfaffe]

Since the 8.0 branch is around the corner I'd really like feedback from @beanz whether this makes sense or not.

[bogner]

I believe this fixes the issues I was hitting.

[chandlerc]

LGTM.

After thinking more about it, this seems like the only sensible course.

Once you set this, you can't really go back, but you can delay setting it and this patch lets exactly that happen. Feel free to go ahead and submit, folks can follow-up post-commit if needed and it addresses an issue impacting Duncan and maybe others.

llvm/cmake/modules/CMakeLists.txt

set(LLVM_CONFIG_INCLUDE_DIRS
   "${LLVM_INCLUDE_DIR}"
   )
 set(LLVM_CONFIG_LIBRARY_DIRS
   "${LLVM_LIBRARY_DIR}"
   )
 set(LLVM_CONFIG_CMAKE_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
 set(LLVM_CONFIG_BINARY_DIR "${LLVM_BINARY_DIR}")
 set(LLVM_CONFIG_TOOLS_BINARY_DIR "${LLVM_TOOLS_BINARY_DIR}")
+
+if (LLVM_LINK_LLVM_DYLIB)
+  set(LLVM_CONFIG_LINK_LLVM_DYLIB
+      "set(LLVM_LINK_LLVM_DYLIB ${LLVM_LINK_LLVM_DYLIB})")
+endif()
+
 # We need to use the full path to the LLVM Exports file to make sure we get the
 # one from the build tree. This is due to our cmake files being split between
 # this source dir and the binary dir in the build tree configuration and the
 # LLVM_CONFIG_CMAKE_DIR being the source directory. In contrast in the install
 # tree, both the generated LLVMExports.cmake file and the rest of the cmake
 # source files are put in the same cmake directory.
 set(LLVM_CONFIG_EXPORTS_FILE "${LLVM_EXPORTS_FILE}")
 set(LLVM_CONFIG_EXPORTS "${LLVM_EXPORTS};${LLVM_EXPORTS_BUILDTREE_ONLY}")

llvm/cmake/modules/LLVMConfig.cmake.in

 # This file provides information and services to the final user.
 
 @LLVM_CONFIG_CODE@
 
 set(LLVM_VERSION_MAJOR @LLVM_VERSION_MAJOR@)
 set(LLVM_VERSION_MINOR @LLVM_VERSION_MINOR@)
 set(LLVM_VERSION_PATCH @LLVM_VERSION_PATCH@)
 set(LLVM_PACKAGE_VERSION @PACKAGE_VERSION@)
 
 set(LLVM_BUILD_TYPE @CMAKE_BUILD_TYPE@)
 
 set(LLVM_COMMON_DEPENDS @LLVM_COMMON_DEPENDS@)
 
 set(LLVM_AVAILABLE_LIBS @LLVM_AVAILABLE_LIBS@)
 
-set(LLVM_LINK_LLVM_DYLIB @LLVM_LINK_LLVM_DYLIB@)
+@LLVM_CONFIG_LINK_LLVM_DYLIB@
 
 set(LLVM_DYLIB_COMPONENTS @LLVM_DYLIB_COMPONENTS@)
 
 set(LLVM_ALL_TARGETS @LLVM_ALL_TARGETS@)
 
 set(LLVM_TARGETS_TO_BUILD @LLVM_TARGETS_TO_BUILD@)
 
 set(LLVM_TARGETS_WITH_JIT @LLVM_TARGETS_WITH_JIT@)