Eliminate strict-aliasing warnings in sha256.c
Eliminate gcc compiler warnings in ieee.c

ieee.c:1481: warning: 's390_integer_lbfp' defined but not used
ieee.c:1499: warning: 's390_integer_sbfp' defined but not used
ieee.c:1481: warning: 'z900_integer_lbfp' defined but not used
ieee.c:1499: warning: 'z900_integer_sbfp' defined but not used