[gcc/trunk] include: Fix -Wundef warnings in ansidecl.h

[gcc/trunk] include: Fix -Wundef warnings in ansidecl.h

[Marek Polacek]

https://gcc.gnu.org/g:34dbb5f346459a1b36cd0cfbfe1cf18cd099fdf3

commit 34dbb5f346459a1b36cd0cfbfe1cf18cd099fdf3
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Jul 20 16:26:28 2021 -0400

    include: Fix -Wundef warnings in ansidecl.h
    
    This quashes -Wundef warnings in ansidecl.h when compiled in C or C++.
    In C, __cpp_constexpr and __cplusplus aren't defined so we evaluate
    them to 0; conversely, __STDC_VERSION__ is not defined in C++.
    This has caused grief when -Wundef is used with -Werror.
    
    I've also tested -traditional-cpp.
    
    include/ChangeLog:
    
            * ansidecl.h: Check if __cplusplus is defined before checking
            the value of __cpp_constexpr and __cplusplus.  Don't check
            __STDC_VERSION__ in C++.

Diff:
---
 include/ansidecl.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/ansidecl.h b/include/ansidecl.h
index 0515228f325..2efe3e85e59 100644
--- a/include/ansidecl.h
+++ b/include/ansidecl.h
@@ -79,7 +79,7 @@ So instead we use the macro below and test it against specific values.  */
 /* inline requires special treatment; it's in C99, and GCC >=2.7 supports
    it too, but it's not in C89.  */
 #undef inline
-#if __STDC_VERSION__ >= 199901L || defined(__cplusplus) || (defined(__SUNPRO_C) && defined(__C99FEATURES__))
+#if (!defined(__cplusplus) && __STDC_VERSION__ >= 199901L) || defined(__cplusplus) || (defined(__SUNPRO_C) && defined(__C99FEATURES__))
 /* it's a keyword */
 #else
 # if GCC_VERSION >= 2007
@@ -356,7 +356,7 @@ So instead we use the macro below and test it against specific values.  */
 #define ENUM_BITFIELD(TYPE) unsigned int
 #endif
 
-#if __cpp_constexpr >= 200704
+#if defined(__cplusplus) && __cpp_constexpr >= 200704
 #define CONSTEXPR constexpr
 #else
 #define CONSTEXPR
@@ -419,7 +419,7 @@ So instead we use the macro below and test it against specific values.  */
 
    so that most attempts at copy are caught at compile-time.  */
 
-#if __cplusplus >= 201103
+#if defined(__cplusplus) && __cplusplus >= 201103
 #define DISABLE_COPY_AND_ASSIGN(TYPE)		\
   TYPE (const TYPE&) = delete;			\
   void operator= (const TYPE &) = delete