[Backend] Establish standalone build infrastructure

Add the thin monorepo CMake entry point and an independently configurable backend project. Enforce the Clang/C++23 toolchain, expose Make/Ninja-neutral tests and developer checks, export an installable RCCBackend package, and introduce the first Support error abstraction.

1 files changed, 28 insertions, 0 deletions

diff --git a/backend/lib/Support/Error.cpp b/backend/lib/Support/Error.cpp
new file mode 100644
index 0000000..dc7d590
--- /dev/null
+++ b/backend/lib/Support/Error.cpp
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "rcc/Support/Error.h"
+
+namespace rcc {
+
+std::string_view getErrorCodeName(ErrorCode Code) noexcept {
+  switch (Code) {
+  case ErrorCode::InvalidArgument:
+    return "invalid argument";
+  case ErrorCode::ParseError:
+    return "parse error";
+  case ErrorCode::VerificationError:
+    return "verification error";
+  case ErrorCode::Unsupported:
+    return "unsupported";
+  case ErrorCode::IoError:
+    return "I/O error";
+  case ErrorCode::InternalError:
+    return "internal error";
+  }
+
+  return "unknown error";
+}
+
+Error::Error(ErrorCode Code, std::string Message) : Code(Code), Message(std::move(Message)) {}
+
+} // namespace rcc