Added [-Wl] to clang_cc_toolchain_config.bzl. fixed issues #1404

[William-Mou]

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When running the example program with LLVM:

INFO: From Linking explorer/explorer:
clang++: warning: argument unused during compilation: '-pie' [-Wunused-command-line-argument]

Temporarily avoid generating warnings with -Wl, but -pie may not need to be used. #1404

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[jonmeow]

I think #2175 addresses this differently, per @chandlerc's suggestion.