A different fix to #218 and DMD2682 that does not lead to constant folding regressions. Fixes run/const_15, run/c/const_16_B. The price is removing the lvalueness of struct literals. If it turns out too much code depends on this behavior or we don't want to break with DMD, we could keep struct literals as lvalues and instead convert struct literals used as expression initializers into struct initializers.

// Copyright (c) 1999-2002 by Digital Mars
// All Rights Reserved
// written by Walter Bright
// www.digitalmars.com

struct GCStats
{
    size_t poolsize;		// total size of pool
    size_t usedsize;		// bytes allocated
    size_t freeblocks;		// number of blocks marked FREE
    size_t freelistsize;		// total of memory on free lists
    size_t pageblocks;		// number of blocks marked PAGE
}