[Driver] Enable outline atomics for OpenBSD/aarch64 (#155713)

Author: brad0

clang/lib/Driver/ToolChains/OpenBSD.h

@@ -79,6 +79,11 @@ class LLVM_LIBRARY_VISIBILITY OpenBSD : public Generic_ELF {
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
 
+  bool IsAArch64OutlineAtomicsDefault(
+      const llvm::opt::ArgList &Args) const override {
+    return true;
+  }
+
   std::string getCompilerRT(const llvm::opt::ArgList &Args, StringRef Component,
                             FileType Type = ToolChain::FT_Static,
                             bool IsFortran = false) const override;

clang/test/Driver/aarch64-features.c

@@ -45,7 +45,7 @@
 // RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-OFF %s
 
 // RUN: %clang --target=aarch64-unknown-openbsd -rtlib=compiler-rt \
-// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-OFF %s
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-ON %s
 
 // RUN: %clang --target=aarch64-linux-gnu -rtlib=libgcc \
 // RUN: --gcc-toolchain=%S/Inputs/aarch64-linux-gnu-tree/gcc-10 \