IAR: decouple linker location from toolkit's bin dir

The implementation in commit 564d527c04 (IAR: Improve error message for
missing license, 2024-08-12, v3.31.0-rc1~234^2) failed for corner cases
in which symlinks were used from a location different from the one in
which the toolkit is shipped with (`<target>/bin`).

In this new implementation, the `<target>` architecture is taken solely
from the compiler NAME itself for all the supported languages and
forwarded to its respective BinUtils executable names
(e.g., `icc<target>`, `iasm<target>`, `a<target>`). This decouples the
location from the subdirectory in which they should be found.

Fixes: #26610

Modules/CMakeFindBinUtils.cmake

@@ -111,10 +111,11 @@ elseif("x${CMAKE_${_CMAKE_PROCESSING_LANGUAGE}_COMPILER_ID}" MATCHES "^x(Open)?W
   list(APPEND _CMAKE_TOOL_VARS LINKER AR)
 
 elseif("x${CMAKE_${_CMAKE_PROCESSING_LANGUAGE}_COMPILER_ID}" MATCHES "^xIAR$")
-  # Get the architecture from the IAR compiler parent directory
-  get_filename_component(__iar_bin_dir "${CMAKE_${_CMAKE_PROCESSING_LANGUAGE}_COMPILER}" DIRECTORY)
-  get_filename_component(__iar_toolkit_dir "${__iar_bin_dir}" DIRECTORY)
-  get_filename_component(__iar_arch_id "${__iar_toolkit_dir}" NAME)
+  # Detect the `<lang>` compiler name
+  get_filename_component(__iar_selected_compiler "${CMAKE_${_CMAKE_PROCESSING_LANGUAGE}_COMPILER}" NAME)
+  # Strip out the `icc`,`iasm`,`a` prefixes and other `_suffixes leaving only the `<target>`
+  string(TOLOWER "${__iar_selected_compiler}" __iar_arch_id)
+  string(REGEX REPLACE "^x(icc|iasm|a)|(_.*)$" "" __iar_arch_id "x${__iar_arch_id}")
   # IAR Archive Tool
   set(_CMAKE_AR_NAMES
     "iarchive" "iarchive.exe"
@@ -147,8 +148,7 @@ elseif("x${CMAKE_${_CMAKE_PROCESSING_LANGUAGE}_COMPILER_ID}" MATCHES "^xIAR$")
     "isymexport" "isymexport.exe"
   )
   list(APPEND _CMAKE_TOOL_VARS AR LINKER IAR_ELFDUMP IAR_ELFTOOL IAR_EXE2OBJ IAR_OBJMANIP IAR_SYMEXPORT)
-  unset(__iar_bin_dir)
-  unset(__iar_toolkit_dir)
+  unset(__iar_selected_compiler)
   unset(__iar_arch_id)
 
 # in all other cases search for ar, ranlib, etc.