Fix LLVM tool --version build mode printing for MSVC

LLVM tools such as llc print "DEBUG build" or "Optimized build" when
passed --version. Before this change, this was implemented by checking
for the __OPTIMIZE__ GCC macro. MSVC does not define this macro. For
MSVC, control this behavior with _DEBUG instead. It doesn't have
precisely the same meaning, but in most configurations, it will do the
right thing.

Fixes PR17752

Reviewed by: MaskRay

Differential Revision: https://reviews.llvm.org/D71817

llvm/lib/Support/CommandLine.cpp

@@ -2436,6 +2436,28 @@ static VersionPrinterTy OverrideVersionPrinter = nullptr;
 
 static std::vector<VersionPrinterTy> *ExtraVersionPrinters = nullptr;
 
+#if defined(__GNUC__)
+// GCC and GCC-compatible compilers define __OPTIMIZE__ when optimizations are
+// enabled.
+# if defined(__OPTIMIZE__)
+#  define LLVM_IS_DEBUG_BUILD 0
+# else
+#  define LLVM_IS_DEBUG_BUILD 1
+# endif
+#elif defined(_MSC_VER)
+// MSVC doesn't have a predefined macro indicating if optimizations are enabled.
+// Use _DEBUG instead. This macro actually corresponds to the choice between
+// debug and release CRTs, but it is a reasonable proxy.
+# if defined(_DEBUG)
+#  define LLVM_IS_DEBUG_BUILD 1
+# else
+#  define LLVM_IS_DEBUG_BUILD 0
+# endif
+#else
+// Otherwise, for an unknown compiler, assume this is an optimized build.
+# define LLVM_IS_DEBUG_BUILD 0
+#endif
+
 namespace {
 class VersionPrinter {
 public:
@@ -2451,7 +2473,7 @@ public:
     OS << " " << LLVM_VERSION_INFO;
 #endif
     OS << "\n  ";
-#ifndef __OPTIMIZE__
+#if LLVM_IS_DEBUG_BUILD
     OS << "DEBUG build";
 #else
     OS << "Optimized build";