runnable/mars1.d: Properly work around LLVM x86 backend bug/limitation

Author: kinke

runnable/mars1.d

@@ -794,23 +794,26 @@ struct S8658
     int[16385] a;
 }
 
+// LDC_FIXME: The LLVM x86 backend suffers from this as well - an
+//            argument's size in bytes seems to be limited to 16 bits.
+version (LDC) version (X86) version = LDC_X86;
+
+version (LDC_X86) {} else
+{
 void foo8658(S8658 s)
 {
     int x;
 }
+}
 
 void test8658()
 {
     S8658 s;
-version (LDC)
-{
-    // LDC_FIXME: The LLVM x86 backend suffers from this as well.
-}
-else
-{
+  version (LDC_X86) {} else
+  {
     for(int i = 0; i < 1000; i++)
         foo8658(s);
-}
+  }
 }
 
 ////////////////////////////////////////////////////////////////////////