[gcc r16-6282] libstdc++: Restore test for generate_cannonical with __float128.

[Tomasz Kaminski]

https://gcc.gnu.org/g:9e56bd1cc971c5a856c97d1f2eb5f9a1dd682cb6

commit r16-6282-g9e56bd1cc971c5a856c97d1f2eb5f9a1dd682cb6
Author: Tomasz Kamiński <tkaminsk@redhat.com>
Date:   Fri Dec 19 15:52:00 2025 +0100

    libstdc++: Restore test for generate_cannonical with __float128.
    
    Accidentally dropped from commit.
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/26_numerics/random/uniform_real_distribution/operators/gencanon_eng.cc:
            Test __float128 when available.

Diff:
---
 .../random/uniform_real_distribution/operators/gencanon_eng.cc       | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/gencanon_eng.cc b/libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/gencanon_eng.cc
index c8d5b5d263be..662e3568a304 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/gencanon_eng.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/gencanon_eng.cc
@@ -36,4 +36,9 @@ int main()
   test_all_engines<float>();
   test_all_engines<double>();
   test_all_engines<long double>();
+#ifndef _GLIBCXX_GENERATE_CANONICAL_STRICT
+#  ifdef __SIZEOF_FLOAT128__
+  test_all_engines<__float128>();
+#  endif
+#endif 
 }