Switch BuildData to char arrays (#5464)

string_view was suggested at
https://github.com/carbon-language/carbon-lang/pull/5451#discussion_r2080640267,
but it turns out it's helpful to be even more hermetic for build
configuration.

common/build_data.cpp

@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "common/build_data.h"
+
+namespace Carbon::BuildData {
+
+const llvm::StringRef Platform = Internal::platform;
+const bool BuildCoverageEnabled = Internal::build_coverage_enabled;
+const llvm::StringRef TargetName = Internal::target_name;
+const llvm::StringRef BuildTarget = Internal::build_target;
+
+}  // namespace Carbon::BuildData