[clang] [clang][Fuchsia] Add test for Fuchsia-specific predefines (PR #194780)

[Roland McGrath via cfe-commits]

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@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -E -dM -triple=aarch64-unknown-fuchsia < /dev/null \
+// RUN:   | FileCheck -match-full-lines -check-prefixes=FUCHSIA %s
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frobtech wrote:

I figured we'd probably eventually have some for arch differences too.

https://github.com/llvm/llvm-project/pull/194780