`--with-nvcc-gencode` help text differs slightly from expected format

[mhrywniak]

Looking at

ucc/config/m4/cuda.m4

Line 30 in cf97156

[AS_HELP_STRING([--with-nvcc-gencode=arch,code],

it says

    AC_ARG_WITH([nvcc-gencode],
                [AS_HELP_STRING([--with-nvcc-gencode=arch,code],
                                [Defines target GPU architecture,
                                 see nvcc -gencode option for details])],

although the sample strings are of the form e.g. ARCH7="-gencode=arch=compute_52,code=sm_52".

I think the help text should be tweaked to say --with-nvcc-gencode="-gencode=arch,code", or potentially the mechanism tweaked to automatically add -gencode=... to all flags.