CMakeFindBinUtils: Always consider plain binutils when not cross-compiling

Since commit c5dd2ca538 (DetermineCompiler: Relax
_CMAKE_TOOLCHAIN_PREFIX detection, 2020-03-25, v3.18.0-rc1~430^2),
`_CMAKE_TOOLCHAIN_PREFIX` may be set even when not cross-compiling.
In this case we may still need to use binutils without any prefix.

Fixes: #21103
1 file changed