math/givaro: only declare std::bool_constant if it does not exist yet

While doing test builds for bug 284159 (math/linbox), I ran into an
issue compiling against one of the math/givaro headers, with clang and
libc++ 19:

  /usr/local/include/givaro/random-integer.h:40:14: error: reference to 'bool_constant' is ambiguous
     40 |         std::bool_constant<_Exact_Size>::type _Exact_Size_t;
        |              ^
  /usr/include/c++/v1/__type_traits/integral_constant.h:42:1: note: candidate found by name lookup is 'std::__1::bool_constant'
     42 | using bool_constant = integral_constant<bool, __b>;
        | ^
  /usr/local/include/givaro/random-integer.h:16:5: note: candidate found by name lookup is 'std::bool_constant'
     16 |     using bool_constant = integral_constant<bool, B>;
        |     ^

The problem is that random-integer.h attempts to declare
std::bool_constant, even though libc++ headers already have this
template.

Conditionalize it on __cpp_lib_bool_constant [1], so it is only declared
when necessary (i.e. if somebody compiles against and older C++
library).

[1] https://en.cppreference.com/w/cpp/feature_test#cpp_lib_bool_constant

PR:		284167
Approved by:	pi (maintainer)
MFH:		2025Q1

math/givaro/files/patch-src_kernel_integer_random-integer.h

@@ -1,6 +1,19 @@
 --- src/kernel/integer/random-integer.h.orig	2021-12-14 10:00:03 UTC
 +++ src/kernel/integer/random-integer.h
-@@ -91,7 +91,6 @@ namespace Givaro
+@@ -11,10 +11,12 @@
+ 
+ #include "gmp++/gmp++.h"
+ 
++#if __cpp_lib_bool_constant < 201505L
+ namespace std {
+     template <bool B>
+     using bool_constant = integral_constant<bool, B>;
+ }
++#endif
+ 
+ namespace Givaro
+ {
+@@ -91,7 +93,6 @@ namespace Givaro
              if (this != &R) {
                  _bits = R._bits;
                  _integer = R._integer;