[clang][Headers] Avoid compiler warnings in builtin headers

While debugging module support using -Wsystem-headers, we discovered that if
-Werror, and -Wundef or -Wmacro-redefined are specified, they can cause errors
to be generated in these builtin headers.

Differential Revision: https://reviews.llvm.org/D130800

Author: ddcc

clang/lib/Headers/float.h

@@ -38,9 +38,10 @@
 #  undef FLT_MANT_DIG
 #  undef DBL_MANT_DIG
 #  undef LDBL_MANT_DIG
-#  if __STDC_VERSION__ >= 199901L || !defined(__STRICT_ANSI__) ||              \
-      __cplusplus >= 201103L ||                                                \
-      (__STDC_HOSTED__ && defined(_AIX) && defined(_ALL_SOURCE))
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
+    !defined(__STRICT_ANSI__) ||                                               \
+    (defined(__cplusplus) && __cplusplus >= 201103L) ||                        \
+    (__STDC_HOSTED__ && defined(_AIX) && defined(_ALL_SOURCE))
 #    undef DECIMAL_DIG
 #  endif
 #  undef FLT_DIG
@@ -67,9 +68,10 @@
 #  undef FLT_MIN
 #  undef DBL_MIN
 #  undef LDBL_MIN
-#  if __STDC_VERSION__ >= 201112L || !defined(__STRICT_ANSI__) ||              \
-      __cplusplus >= 201703L ||                                                \
-      (__STDC_HOSTED__ && defined(_AIX) && defined(_ALL_SOURCE))
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) ||              \
+    !defined(__STRICT_ANSI__) ||                                               \
+    (defined(__cplusplus) && __cplusplus >= 201703L) ||                        \
+    (__STDC_HOSTED__ && defined(_AIX) && defined(_ALL_SOURCE))
 #    undef FLT_TRUE_MIN
 #    undef DBL_TRUE_MIN
 #    undef LDBL_TRUE_MIN
@@ -92,8 +94,9 @@
 #define DBL_MANT_DIG __DBL_MANT_DIG__
 #define LDBL_MANT_DIG __LDBL_MANT_DIG__
 
-#if __STDC_VERSION__ >= 199901L || !defined(__STRICT_ANSI__) ||                \
-    __cplusplus >= 201103L ||                                                  \
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
+    !defined(__STRICT_ANSI__) ||                                               \
+    (defined(__cplusplus) && __cplusplus >= 201103L) ||                        \
     (__STDC_HOSTED__ && defined(_AIX) && defined(_ALL_SOURCE))
 #  define DECIMAL_DIG __DECIMAL_DIG__
 #endif
@@ -130,8 +133,9 @@
 #define DBL_MIN __DBL_MIN__
 #define LDBL_MIN __LDBL_MIN__
 
-#if __STDC_VERSION__ >= 201112L || !defined(__STRICT_ANSI__) ||                \
-    __cplusplus >= 201703L ||                                                  \
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) ||              \
+    !defined(__STRICT_ANSI__) ||                                               \
+    (defined(__cplusplus) && __cplusplus >= 201703L) ||                        \
     (__STDC_HOSTED__ && defined(_AIX) && defined(_ALL_SOURCE))
 #  define FLT_TRUE_MIN __FLT_DENORM_MIN__
 #  define DBL_TRUE_MIN __DBL_DENORM_MIN__

clang/lib/Headers/limits.h

@@ -65,7 +65,7 @@
 /* C2x 5.2.4.2.1 */
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 #define BOOL_WIDTH   __BOOL_WIDTH__
 #define CHAR_WIDTH   CHAR_BIT
 #define SCHAR_WIDTH  CHAR_BIT
@@ -93,7 +93,8 @@
 /* C99 5.2.4.2.1: Added long long.
    C++11 18.3.3.2: same contents as the Standard C Library header <limits.h>.
  */
-#if __STDC_VERSION__ >= 199901L || __cplusplus >= 201103L
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
+    (defined(__cplusplus) && __cplusplus >= 201103L)
 
 #undef  LLONG_MIN
 #undef  LLONG_MAX

clang/lib/Headers/stdarg.h

@@ -23,7 +23,9 @@ typedef __builtin_va_list va_list;
  */
 #define __va_copy(d,s) __builtin_va_copy(d,s)
 
-#if __STDC_VERSION__ >= 199901L || __cplusplus >= 201103L || !defined(__STRICT_ANSI__)
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
+    (defined(__cplusplus) && __cplusplus >= 201103L) ||                        \
+    !defined(__STRICT_ANSI__)
 #define va_copy(dest, src)  __builtin_va_copy(dest, src)
 #endif
 

clang/lib/Headers/stdatomic.h

@@ -45,7 +45,8 @@ extern "C" {
 /* 7.17.2 Initialization */
 
 #define ATOMIC_VAR_INIT(value) (value)
-#if (__STDC_VERSION__ >= 201710L || __cplusplus >= 202002L) &&                 \
+#if ((defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201710L) ||             \
+     (defined(__cplusplus) && __cplusplus >= 202002L)) &&                      \
     !defined(_CLANG_DISABLE_CRT_DEPRECATION_WARNINGS)
 /* ATOMIC_VAR_INIT was deprecated in C17 and C++20. */
 #pragma clang deprecated(ATOMIC_VAR_INIT)

clang/lib/Headers/stdbool.h

@@ -12,7 +12,7 @@
 
 #define __bool_true_false_are_defined 1
 
-#if __STDC_VERSION__ > 201710L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ > 201710L
 /* FIXME: We should be issuing a deprecation warning here, but cannot yet due
  * to system headers which include this header file unconditionally.
  */
@@ -23,7 +23,7 @@
 #elif defined(__GNUC__) && !defined(__STRICT_ANSI__)
 /* Define _Bool as a GNU extension. */
 #define _Bool bool
-#if __cplusplus < 201103L
+#if defined(__cplusplus) && __cplusplus < 201103L
 /* For C++98, define bool, false, true as a GNU extension. */
 #define bool bool
 #define false false

clang/lib/Headers/stddef.h

@@ -98,7 +98,8 @@ using ::std::nullptr_t;
 #endif /* defined(__need_NULL) */
 
 #if defined(__need_STDDEF_H_misc)
-#if __STDC_VERSION__ >= 201112L || __cplusplus >= 201103L
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) ||              \
+    (defined(__cplusplus) && __cplusplus >= 201103L)
 #include "__stddef_max_align_t.h"
 #endif
 #define offsetof(t, d) __builtin_offsetof(t, d)