GN: Don't pass -integrated-as to pnacl-clang
GN: Don't pass -integrated-as to pnacl-clang

The -integrated-as switch is desireable for nacl-clang, but it is
meaningless for (and not accepted by) pnacl-clang.  So don't treat
the pnacl case the same as the nacl-clang case.

BUG= 531702
R=dpranke@chromium.org, dschuff@chromium.org

Review URL: https://codereview.chromium.org/1387253005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#353467}

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