[clang] [clang] Add support for SerenityOS (PR #187941)

[Fangrui Song via cfe-commits]

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@@ -329,3 +329,11 @@
 // RUN:   | FileCheck %s --check-prefix=CHECK-PIC2
 // RUN: %clang -c %s --target=i586-pc-haiku -### 2>&1 \
 // RUN:   | FileCheck %s --check-prefix=CHECK-PIC2
+
+// Serenity has PIC and PIE by default
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MaskRay wrote:

Delete from this test. Just test the option in the dedicated serenity.cpp

https://github.com/llvm/llvm-project/pull/187941