Due to tile missing a bunch of FP exception and rounding
support, the tests generate warnings. These changes fix the
warnings by just not compiling some unused functions, and
adding some attribute ((unused)) tags.
This patch fixes warnings of the form "tst-printf-round.c:202:17:
warning: passing argument 3 of 'test_hex_in_one_mode' discards 'const'
qualifier from pointer target type", by adding an extra const to that
argument (so that after array-to-pointer conversion it's const char
*const *).
Tested for x86_64.
* stdio-common/tst-printf-round.c (test_hex_in_one_mode): Make
third argument const.
