Quick fix for bswap cannot be interpreted at compile time

Author: AlexeyProkhin

dmd2/builtin.c

@@ -203,7 +203,12 @@ void builtin_init()
     add_builtin("_D4core5bitop3bsrFNaNbNfmZi", &eval_bsr);
 
     // @safe pure nothrow uint function(uint)
+#if IN_LLVM
+    // bswap is intrinsic and isn't mangled
+    add_builtin("bswap", &eval_bswap);
+#else
     add_builtin("_D4core5bitop5bswapFNaNbNfkZk", &eval_bswap);
+#endif
 }
 
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