fix some Wundef warnings in public headers

llvm/include/llvm/ADT/Statistic.h

 #include <memory>
 #include <vector>
 
 // Determine whether statistics should be enabled. We must do it here rather
 // than in CMake because multi-config generators cannot determine this at
 // configure time.
 #if !defined(NDEBUG) || LLVM_FORCE_ENABLE_STATS
 #define LLVM_ENABLE_STATS 1
+#else
+#define LLVM_ENABLE_STATS 0
 #endif
 
 namespace llvm {
 
 class raw_ostream;
 class raw_fd_ostream;
 class StringRef;
 

llvm/include/llvm/Config/abi-breaking.h.cmake

 /* Define to enable checks that alter the LLVM C++ ABI */
 #cmakedefine01 LLVM_ENABLE_ABI_BREAKING_CHECKS
 
 /* Define to enable reverse iteration of unordered llvm containers */
 #cmakedefine01 LLVM_ENABLE_REVERSE_ITERATION
 
 /* Allow selectively disabling link-time mismatch checking so that header-only
    ADT content from LLVM can be used without linking libSupport. */
-#if !LLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING
+#if !defined(LLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING) || !LLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING
 
 // ABI_BREAKING_CHECKS protection: provides link-time failure when clients build
 // mismatch with LLVM
 #if defined(_MSC_VER)
 // Use pragma with MSVC
 #define LLVM_XSTR(s) LLVM_STR(s)
 #define LLVM_STR(s) #s
 #pragma detect_mismatch("LLVM_ENABLE_ABI_BREAKING_CHECKS", LLVM_XSTR(LLVM_ENABLE_ABI_BREAKING_CHECKS))