clang: Use rtlib provided by compiler instead of hardcoding libgcc

Clang provides runtime library `libclang_rt.builtins.<arch>.a` but
`libgcc.a` is also supported.

The compiler can provide full path to the selected library using the
`--print-libgcc-file-name` option, for example:
```
/usr/lib64/clang/17/lib/baremetal/libclang_rt.builtins-armv7m.a
```

If `--rtlib=libgcc` option is provided, clang will also provide
appropriate path.

This patch replaces hardcoded `libgcc` with library name extracted from
path, so we are compatible with both libraries.

Signed-off-by: Patryk Duda <pdk@semihalf.com>

cmake/compiler/clang/target.cmake

@@ -58,16 +58,16 @@ if(NOT "${ARCH}" STREQUAL "posix")
   # This libgcc code is partially duplicated in compiler/*/target.cmake
   execute_process(
     COMMAND ${CMAKE_C_COMPILER} ${TOOLCHAIN_C_FLAGS} --print-libgcc-file-name
-    OUTPUT_VARIABLE LIBGCC_FILE_NAME
+    OUTPUT_VARIABLE RTLIB_FILE_NAME
     OUTPUT_STRIP_TRAILING_WHITESPACE
     )
 
-  get_filename_component(LIBGCC_DIR ${LIBGCC_FILE_NAME} DIRECTORY)
+  get_filename_component(RTLIB_DIR ${RTLIB_FILE_NAME} DIRECTORY)
+  get_filename_component(RTLIB_NAME_WITH_PREFIX ${RTLIB_FILE_NAME} NAME_WLE)
+  string(REPLACE lib "" RTLIB_NAME ${RTLIB_NAME_WITH_PREFIX})
 
-  list(APPEND LIB_INCLUDE_DIR "-L\"${LIBGCC_DIR}\"")
-  if(LIBGCC_DIR)
-    list(APPEND TOOLCHAIN_LIBS gcc)
-  endif()
+  list(APPEND LIB_INCLUDE_DIR -L${RTLIB_DIR})
+  list(APPEND TOOLCHAIN_LIBS ${RTLIB_NAME})
 
   list(APPEND CMAKE_REQUIRED_FLAGS -nostartfiles -nostdlib ${isystem_include_flags})
   string(REPLACE ";" " " CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")