include/ruby/3: do not skip RUBY3_UNREACHABLE_RETURN

Revert "Revert "include/ruby/3/core/rtypeddata.h: Use 0 instead of NULL for C++ compiler""
Revert "include/ruby/3/core/rtypeddata.h: Use 0 instead of NULL for C++ compiler"
Revert "include/ruby/3: Skip RUBY3_UNREACHABLE_RETURN for icc"
Revert "include/ruby/3: Stop RUBY3_UNREACHABLE_RETURN to suppress a SunC warning"

This reverts commit b965e7e05e.
This reverts commit d2bb2e066b.
This reverts commit 8ab4c55e7a.
This reverts commit 78eec3cdc5.

After https://github.com/ruby/ruby/pull/3011, we no longer need these
ifdef guards.

include/ruby/3/core/rtypeddata.h

@@ -160,9 +160,7 @@ RTYPEDDATA_TYPE(VALUE obj)
 #if ! RUBY_NDEBUG
     if (RB_UNLIKELY(! RTYPEDDATA_P(obj))) {
         rb_unexpected_type(obj, RUBY_T_DATA);
-# if ! defined(__sun) && ! RUBY3_COMPILER_IS(Intel)
         RUBY3_UNREACHABLE_RETURN(NULL);
-# endif
     }
 #endif
 

include/ruby/3/memory.h

@@ -253,9 +253,7 @@ ruby3_size_mul_or_raise(size_t x, size_t y)
     }
     else {
         ruby_malloc_size_overflow(x, y);
-# if ! defined(__sun) && ! RUBY3_COMPILER_IS(Intel)
         RUBY3_UNREACHABLE_RETURN(0);
-# endif
     }
 }