Build warnings

[hughperkins]

• unused variable err, see example 1 below
• narrowing conversion of nthreads from int to size_t
• `ISO c++98 does not support the 'c' gnu_printf length modifier1

example 1:

clMathLibraries/clBLAS/src/library/blas/functor/include/functor.h:67:16: warning: unused variable ‘err’ [-Wunused-variable]
         cl_int err = clSetKernelArg(kernel,

example 2:

clMathLibraries/clBLAS/src/library/blas/functor/gpu_dtrsm.cc:285:42: warning: narrowing conversion of ‘nthreads’ from ‘int’ to ‘size_t {aka long unsigned int}’ inside { } is ill-formed in C++11 [-Wnarrowing]
     size_t globalThreads[1] = { nthreads };

example 3:

clMathLibraries/clBLAS/src/library/blas/gens/symm_cached.cpp:196:35: warning: ISO C++98 does not support the ‘z’ gnu_printf length modifier [-Wformat=]
  sprintf(width, "%" SPREFIX "u", Y);