Fix return type scoping issue identified by more recent version of GCC.
Fix return type scoping issue identified by more recent version of GCC.

Winterflower/khmer,jas14/khmer,kdmurray91/khmer,ged-lab/khmer,ged-lab/khmer,souravsingh/khmer,ged-lab/khmer,Winterflower/khmer,kdmurray91/khmer,jas14/khmer,F1000Research/khmer,souravsingh/khmer,F1000Research/khmer,kdmurray91/khmer,Winterflower/khmer,souravsingh/khmer,F1000Research/khmer,jas14/khmer