ld, nm: Silence on-by-default warnings

[tob2]

When compiling nvptx-tools with default settings, the following warnings are printed, which this commit silences:

nvptx-ld.cc:878:20 and nvptx-nm.cc:670:20:
In function ‘int main(int, char**)’:
warning: comparison of integer expressions of different signedness:
‘size_t’ {aka ‘long unsigned int’} and ‘off_t’ {aka ‘long int’}
[-Wsign-compare]

nvptx-nm.cc:386:14:
warning: unnecessary parentheses in declaration of ‘sorters’
[-Wparentheses]
nvptx-nm.cc:386:14: note: remove parentheses

nvptx-nm.cc:464:72:
In function ‘void display_rel_file(std::__cxx11::list<htab*>&,
const std::string&)’:
warning: unused parameter ‘name’ [-Wunused-parameter]

@tschwinge