[driver] Make --version show if assertions, etc. are enabled (#87585)

It's useful to have some significant build options visible in the
version when investigating problems with a specific compiler artifact.
This makes it easy to see if assertions, expensive checks, sanitizers,
etc. are enabled when checking a compiler version.

Example config line output:
Build configuration: +unoptimized, +assertions, +asan, +ubsan

1 files changed, 46 insertions, 0 deletions

diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
index c076ae8..056340b 100644
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -2734,6 +2734,52 @@ void cl::PrintHelpMessage(bool Hidden, bool Categorized) {
     CommonOptions->CategorizedHiddenPrinter.printHelp();
 }
 
+ArrayRef<StringRef> cl::getCompilerBuildConfig() {
+  static const StringRef Config[] = {
+      // Placeholder to ensure the array always has elements, since it's an
+      // error to have a zero-sized array. Slice this off before returning.
+      "",
+  // Actual compiler build config feature list:
+#if LLVM_IS_DEBUG_BUILD
+      "+unoptimized",
+#endif
+#ifndef NDEBUG
+      "+assertions",
+#endif
+#ifdef EXPENSIVE_CHECKS
+      "+expensive-checks",
+#endif
+#if __has_feature(address_sanitizer)
+      "+asan",
+#endif
+#if __has_feature(dataflow_sanitizer)
+      "+dfsan",
+#endif
+#if __has_feature(hwaddress_sanitizer)
+      "+hwasan",
+#endif
+#if __has_feature(memory_sanitizer)
+      "+msan",
+#endif
+#if __has_feature(thread_sanitizer)
+      "+tsan",
+#endif
+#if __has_feature(undefined_behavior_sanitizer)
+      "+ubsan",
+#endif
+  };
+  return ArrayRef(Config).drop_front(1);
+}
+
+// Utility function for printing the build config.
+void cl::printBuildConfig(raw_ostream &OS) {
+#if LLVM_VERSION_PRINTER_SHOW_BUILD_CONFIG
+  OS << "Build config: ";
+  llvm::interleaveComma(cl::getCompilerBuildConfig(), OS);
+  OS << '\n';
+#endif
+}
+
 /// Utility function for printing version number.
 void cl::PrintVersionMessage() {
   CommonOptions->VersionPrinterInstance.print(CommonOptions->ExtraVersionPrinters);