Skip ROCm's private LLVM when configuring Iridium

find_package(LLVM CONFIG) also searches <prefix>/llvm/lib/cmake/llvm for
every PATH entry, before the system prefixes. With /opt/rocm/bin on PATH
it found ROCm's LLVM 22.0.0git, whose llvm-config reports no shared
library, and 6d6159b's fallback to the llvm-config on PATH then rejected
the system LLVM 23 because its major differs from the ROCm headers, so a
fresh configure failed (issue #1).

Before find_package, keep LLVM_DIR only if the llvm-config next to it
reports a shared library; otherwise, or when LLVM_DIR is unset, use the
llvm-config on PATH that does and take its --cmakedir. A working pinned
LLVM_DIR is left alone.

Checked with a fake ROCm prefix on PATH: plain find_package picks it;
the new code picks /usr/lib/cmake/llvm (LLVM 23) on a fresh configure,
replaces a cached ROCm LLVM_DIR, and keeps a working cached
/usr/lib64/cmake/llvm. A standalone configure of Indium with the fake
ROCm on PATH completes with the system LLVM.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

patches/metal--deps--indium.patch

@@ -8629,10 +8629,53 @@ new file mode 100644
 +	}
 +}
 diff --git a/CMakeLists.txt b/CMakeLists.txt
-index 8d95863..603dc3d 100644
+index 8d95863..1af3167 100644
 --- a/CMakeLists.txt
 +++ b/CMakeLists.txt
-@@ -159,9 +159,33 @@ if (NOT DARLING)
+@@ -2,6 +2,41 @@ project(indium)
+ cmake_minimum_required(VERSION 3.20)
+ 
+ find_package(Vulkan REQUIRED)
++
++# Iridium compiles against these LLVM headers and loads the shared libLLVM of the same major at run time, so the LLVM
++# found here needs an llvm-config that reports a shared library. find_package also looks in <prefix>/llvm/lib/cmake/llvm
++# for every PATH entry, so with /opt/rocm/bin on PATH it picks ROCm's private LLVM ahead of the system one, and a cached
++# LLVM_DIR can name an LLVM that was removed since. Unless LLVM_DIR names a usable LLVM, use the llvm-config on PATH.
++function(indium_llvm_config_works tool result)
++	set(${result} FALSE PARENT_SCOPE)
++	execute_process(COMMAND "${tool}" --link-shared --libnames
++		OUTPUT_VARIABLE libname RESULT_VARIABLE status ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
++	if (status EQUAL 0 AND libname)
++		set(${result} TRUE PARENT_SCOPE)
++	endif()
++endfunction()
++
++set(indium_llvm_usable FALSE)
++if (LLVM_DIR)
++	# <prefix>/lib/cmake/llvm or <prefix>/lib64/cmake/llvm
++	get_filename_component(indium_llvm_prefix "${LLVM_DIR}/../../.." ABSOLUTE)
++	indium_llvm_config_works("${indium_llvm_prefix}/bin/llvm-config" indium_llvm_usable)
++endif()
++if (NOT indium_llvm_usable)
++	find_program(INDIUM_PATH_LLVM_CONFIG llvm-config)
++	if (INDIUM_PATH_LLVM_CONFIG)
++		indium_llvm_config_works("${INDIUM_PATH_LLVM_CONFIG}" indium_path_llvm_usable)
++		execute_process(COMMAND "${INDIUM_PATH_LLVM_CONFIG}" --cmakedir
++			OUTPUT_VARIABLE indium_path_llvm_dir RESULT_VARIABLE indium_status ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
++		if (indium_path_llvm_usable AND indium_status EQUAL 0 AND EXISTS "${indium_path_llvm_dir}")
++			if (LLVM_DIR)
++				message(STATUS "LLVM_DIR=${LLVM_DIR} has no llvm-config with a shared library; using ${indium_path_llvm_dir}")
++			endif()
++			set(LLVM_DIR "${indium_path_llvm_dir}" CACHE PATH "The directory containing a CMake configuration file for LLVM." FORCE)
++		endif()
++	endif()
++endif()
++
+ find_package(LLVM REQUIRED CONFIG)
+ 
+ if (DARLING)
+@@ -158,11 +193,35 @@ if (NOT DARLING)
+ 	)
  endif()
  
 -execute_process(
@@ -8667,10 +8710,11 @@ index 8d95863..603dc3d 100644
 +endforeach()
 +if (NOT HOST_LLVM_LIBNAME)
 +	message(FATAL_ERROR "No working llvm-config for LLVM ${LLVM_VERSION} (LLVM_DIR=${LLVM_DIR}). "
-+		"Remove LLVM_DIR from the CMake cache or install the matching LLVM.")
++		"Install an LLVM with a shared libLLVM, or pass -DLLVM_DIR=<its lib/cmake/llvm directory>.")
 +endif()
  
  target_compile_definitions(iridium PRIVATE
+ 	"HOST_LLVM_LIBNAME=\"${HOST_LLVM_LIBNAME}\""
 diff --git a/src/iridium/dynamic-llvm.cpp b/src/iridium/dynamic-llvm.cpp
 index 1b5876e..03af560 100644
 --- a/src/iridium/dynamic-llvm.cpp