Revert "[RISCV] Implement multi-lib reuse rule for RISC-V bare-metal … (#75789)

…toolchain (#73765)"

This reverts commit 111a2290,

as it broke several bots
  https://lab.llvm.org/buildbot/#/builders/245/builds/18162
  https://lab.llvm.org/buildbot/#/builders/188/builds/39436
  https://lab.llvm.org/buildbot/#/builders/187/builds/13723
  https://lab.llvm.org/buildbot/#/builders/182/builds/8449
  https://lab.llvm.org/buildbot/#/builders/198/builds/7438
  https://lab.llvm.org/buildbot/#/builders/176/builds/7419
  https://lab.llvm.org/buildbot/#/builders/186/builds/13781
  https://lab.llvm.org/buildbot/#/builders/183/builds/18116
  https://lab.llvm.org/buildbot/#/builders/197/builds/11410
  https://lab.llvm.org/buildbot/#/builders/184/builds/8651

When reapplying, please take care of another commit that have been
merged after this one:
c7cdf3cd [clang] Use 'starts_with' instead of 'startswith' in
Gnu.cpp (NFC)