Disable failed_constexpr_test for GCC/UBSAN

test/Jamfile.v2

@@ -75,7 +75,9 @@ system-run generic_category_test.cpp ;
 system-run system_category_test.cpp ;
 system-run after_main_test.cpp ;
 system-run failed_test.cpp ;
-system-run failed_constexpr_test.cpp ;
+run failed_constexpr_test.cpp : : :
+    # GCC w/ UBSAN doesn't consider `cat_ != 0` a constant expression
+    <toolset>gcc,<undefined-sanitizer>norecover:<build>no ;
 
 # Quick (CI) test
 run quick.cpp ;