[llvm-libgcc] Fix libgcc.a symlink path when LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=OFFusers/kraj/llvm-libgcc-symlink-fixes

The llvm-libgcc installation was creating incorrect symlinks for libgcc.a
when built with LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=OFF, particularly seen with
Yocto cross-compilation environments.

Issues seen:

-  Absolute path in symlink: The previous code didn't handle absolute paths
   returned by get_compiler_rt_install_dir() in staging/sysroot environments,
   resulting in symlinks like:
   libgcc.a -> /absolute/path/to/sysroot/usr/lib/clang/.../libclang_rt.builtins.a

-  Missing architecture suffix: When the install path contained "clang", the
   code would skip setting builtins_suffix, creating:
   libgcc.a -> clang/21.1.4/lib/linux/libclang_rt.builtins.a
   instead of:
   libgcc.a -> clang/21.1.4/lib/linux/libclang_rt.builtins-aarch64.a

-  Incorrect relative path calculation: The original regex stripped too much
   or too little of the path, either creating symlinks pointing to non-existent
   locations or stripping the clang/ directory prefix entirely.

Solution:

- Extract the relative path starting from 'clang/' when present in absolute
  paths, ensuring the symlink points to the correct location within the
  installation hierarchy
- Always append the architecture suffix to the builtins library name
- Only prepend '../' to the path when LLVM_ENABLE_PER_TARGET_RUNTIME_DIR is
  enabled, as this is when the builtins are in a different directory level

The symlink now correctly points to the existing compiler-rt builtins library
without creating duplicate copies.

Tested with LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=OFF in cross-compilation
environments (aarch64 target).

1 files changed, 20 insertions, 4 deletions

diff --git a/llvm-libgcc/CMakeLists.txt b/llvm-libgcc/CMakeLists.txt
index cd9c5011d410..ee7fe768bda0 100644
--- a/llvm-libgcc/CMakeLists.txt
+++ b/llvm-libgcc/CMakeLists.txt
@@ -124,11 +124,27 @@ target_link_libraries(unwind_shared PUBLIC
 #===============================================================================
 
 get_compiler_rt_install_dir(${COMPILER_RT_DEFAULT_TARGET_ARCH} install_dir_builtins)
-string(REGEX REPLACE "^lib/" "" install_dir_builtins "${install_dir_builtins}")
-string(FIND "${install_dir_builtins}" "clang" install_path_contains_triple)
-if(install_path_contains_triple EQUAL -1)
-  set(builtins_suffix "-${COMPILER_RT_DEFAULT_TARGET_ARCH}")
+
+# Extract the relative path starting from 'clang' or after 'lib/'
+if(IS_ABSOLUTE "${install_dir_builtins}")
+  # For absolute paths, extract starting from 'clang/' if it exists
+  string(REGEX MATCH "clang/.*$" install_dir_builtins_temp "${install_dir_builtins}")
+  if(install_dir_builtins_temp)
+    set(install_dir_builtins "${install_dir_builtins_temp}")
+  else()
+    # Fallback: strip up to first lib/
+    string(REGEX REPLACE "^.*/lib/" "" install_dir_builtins "${install_dir_builtins}")
+  endif()
 else()
+  string(REGEX REPLACE "^lib/" "" install_dir_builtins "${install_dir_builtins}")
+endif()
+
+# Always add the architecture suffix
+set(builtins_suffix "-${COMPILER_RT_DEFAULT_TARGET_ARCH}")
+
+# Only prepend ../ when using per-target runtime directories
+string(FIND "${install_dir_builtins}" "clang" install_path_contains_triple)
+if(install_path_contains_triple GREATER -1 AND LLVM_ENABLE_PER_TARGET_RUNTIME_DIR)
   string(PREPEND install_dir_builtins "../")
 endif()
 set(LLVM_LIBGCC_COMPILER_RT ${install_dir_builtins}/libclang_rt.builtins${builtins_suffix}.a)