Revert "[compiler-rt] Check for and use -lunwind when linking with -nodefaultlibs (#65912)"

This reverts commit 64c0bdd.

This seems to run into errors on some buildbots; configure errors
out like this:

    -- Looking for _Unwind_RaiseException in unwind
    -- Looking for _Unwind_RaiseException in unwind - not found
    CMake Error at /usr/share/cmake-3.25/Modules/CheckLibraryExists.cmake:71 (try_compile):
      Only libraries may be used as try_compile or try_run IMPORTED
      LINK_LIBRARIES.  Got unwind of type UTILITY.
    Call Stack (most recent call first):
      /b/sanitizer-aarch64-linux-fuzzer/build/llvm-project/compiler-rt/cmake/config-ix.cmake:66 (check_library_exists)
      /b/sanitizer-aarch64-linux-fuzzer/build/llvm-project/compiler-rt/CMakeLists.txt:281 (include)

Author: mstorsjo

compiler-rt/cmake/config-ix.cmake

@@ -63,12 +63,6 @@ if (C_SUPPORTS_NODEFAULTLIBS_FLAG)
                         moldname mingwex msvcrt)
     list(APPEND CMAKE_REQUIRED_LIBRARIES ${MINGW_LIBRARIES})
   endif()
-  check_library_exists(unwind _Unwind_RaiseException "" COMPILER_RT_HAS_LIBUNWIND)
-  if (COMPILER_RT_HAS_LIBUNWIND)
-    # If we're omitting default libraries, we might need to manually link in libunwind.
-    # This can affect whether we detect a statically linked libc++ correctly.
-    list(APPEND CMAKE_REQUIRED_LIBRARIES unwind)
-  endif()
 endif ()
 
 # CodeGen options.