[libclc] [libclc] Fix installed symlinks to be relative again (PR #149728)

[Michał Górny via cfe-commits]

https://github.com/mgorny created https://github.com/llvm/llvm-project/pull/149728

Fix the symlink creation logic to use relative paths instead of absolute, in order to ensure that the installed symlinks actually refer to the installed .bc files rather than the ones from the build directory.  This was broken in #146833.  The change is a bit roundabout but it attempts to preserve the spirit of #146833, that is the ability to use multiple output directories (provided they all resides in `${LIBCLC_OUTPUT_LIBRARY_DIR}` and preserve the same structure in the installed tree).

>From 3c28e5c80826a86b66b08a40cb900f70fdcc9a47 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20G=C3=B3rny?= <mgorny at gentoo.org>
Date: Sun, 20 Jul 2025 20:27:23 +0200
Subject: [PATCH] [libclc] Fix installed symlinks to be relative again
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Fix the symlink creation logic to use relative paths instead
of absolute, in order to ensure that the installed symlinks actually
refer to the installed .bc files rather than the ones from the build
directory.  This was broken in #146833.  The change is a bit roundabout
but it attempts to preserve the spirit of #146833, that is the ability
to use multiple output directories (provided they all resides
in `${LIBCLC_OUTPUT_LIBRARY_DIR}` and preserve the same structure
in the installed tree).

Signed-off-by: Michał Górny <mgorny at gentoo.org>
---
 libclc/cmake/modules/AddLibclc.cmake | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/libclc/cmake/modules/AddLibclc.cmake b/libclc/cmake/modules/AddLibclc.cmake
index 056706ee629cd..dc4b1e8286ec0 100644
--- a/libclc/cmake/modules/AddLibclc.cmake
+++ b/libclc/cmake/modules/AddLibclc.cmake
@@ -425,17 +425,21 @@ function(add_libclc_builtin_set)
       WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} )
   endif()
 
-  if(CMAKE_HOST_UNIX OR LLVM_USE_SYMLINKS)
-    set(LIBCLC_LINK_OR_COPY create_symlink)
-  else()
-    set(LIBCLC_LINK_OR_COPY copy)
-  endif()
-
   foreach( a IN LISTS ARG_ALIASES )
+    if(CMAKE_HOST_UNIX OR LLVM_USE_SYMLINKS)
+      cmake_path(RELATIVE_PATH libclc_builtins_lib
+        BASE_DIRECTORY ${LIBCLC_OUTPUT_LIBRARY_DIR}
+        OUTPUT_VARIABLE LIBCLC_LINK_OR_COPY_SOURCE)
+      set(LIBCLC_LINK_OR_COPY create_symlink)
+    else()
+      set(LIBCLC_LINK_OR_COPY_SOURCE ${libclc_builtins_lib})
+      set(LIBCLC_LINK_OR_COPY copy)
+    endif()
+
     set( alias_suffix "${a}-${ARG_TRIPLE}.bc" )
     add_custom_command(
       OUTPUT ${LIBCLC_OUTPUT_LIBRARY_DIR}/${alias_suffix}
-      COMMAND ${CMAKE_COMMAND} -E ${LIBCLC_LINK_OR_COPY} ${libclc_builtins_lib} ${LIBCLC_OUTPUT_LIBRARY_DIR}/${alias_suffix}
+      COMMAND ${CMAKE_COMMAND} -E ${LIBCLC_LINK_OR_COPY} ${LIBCLC_LINK_OR_COPY_SOURCE} ${LIBCLC_OUTPUT_LIBRARY_DIR}/${alias_suffix}
       DEPENDS prepare-${obj_suffix}
     )
     add_custom_target( alias-${alias_suffix} ALL