Warnings in nc_perf code tst_create_files.c and bm_file.c

[edwardhartnett]

I'm seeing some of these new warnings in nc_perf directory, where I am adding a test. I will fix and submit as part of my next PR.

tst_create_files.c: In function ‘main’:
tst_create_files.c:285:31: warning: ‘%s’ directive writing up to 256 bytes into a region of size 253 [-Wformat-overflow=]
  285 |       sprintf(file_name, "tst_%s2_%dD.nc", type_name[t], ndims);
      |                               ^~
tst_create_files.c:285:7: note: ‘sprintf’ output between 12 and 278 bytes into a destination of size 257
  285 |       sprintf(file_name, "tst_%s2_%dD.nc", type_name[t], ndims);
      |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tst_create_files.c:173:31: warning: ‘%s’ directive writing up to 256 bytes into a region of size 253 [-Wformat-overflow=]
  173 |       sprintf(file_name, "tst_%s2_%dD.nc", type_name[t], ndims);
      |                               ^~
tst_create_files.c:173:7: note: ‘sprintf’ output between 12 and 278 bytes into a destination of size 257
  173 |       sprintf(file_name, "tst_%s2_%dD.nc", type_name[t], ndims);
      |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/bin/bash ../libtool  --tag=CC   --mode=link mpicc  -g -Wall ../liblib/libnetcdf.la -L/usr/local/hdf5-1.10.6_szip_mpich/lib -o tst_create_files tst_create_files.o ../liblib/libnetcdf.la -lhdf5_hl -lhdf5 -lm -ldl -lz -lcurl 
libtool: link: mpicc -g -Wall -o tst_create_files tst_create_files.o   -L/usr/local/hdf5-1.10.6_szip_mpich/lib -L/usr/local/szip-2.1.1/lib ../liblib/.libs/libnetcdf.a /usr/local/hdf5-1.10.6_szip_mpich/lib/libhdf5_hl.so /usr/local/hdf5-1.10.6_szip_mpich/lib/libhdf5.so /usr/local/szip-2.1.1/lib/libsz.so -lm -ldl -lz /usr/lib/x86_64-linux-gnu/libcurl.so -pthread -Wl,-rpath -Wl,/usr/local/hdf5-1.10.6_szip_mpich/lib -Wl,-rpath -Wl,/usr/local/szip-2.1.1/lib -Wl,-rpath -Wl,/usr/local/hdf5-1.10.6_szip_mpich/lib -Wl,-rpath -Wl,/usr/local/szip-2.1.1/lib
depbase=`echo bm_file.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`;\
mpicc -DHAVE_CONFIG_H -I. -I..  -I../include -I../oc2 -I/usr/local/hdf5-1.10.6_szip_mpich/include  -g -Wall -MT bm_file.o -MD -MP -MF $depbase.Tpo -c -o bm_file.o bm_file.c &&\
mv -f $depbase.Tpo $depbase.Po
bm_file.c: In function ‘main’:
bm_file.c:1078:39: warning: ‘%s’ directive writing up to 256 bytes into a region of size 248 [-Wformat-overflow=]
 1078 |         sprintf(file_out_2, "tst_copy_%s", file_out);
      |                                       ^~   ~~~~~~~~
bm_file.c:1078:9: note: ‘sprintf’ output between 10 and 266 bytes into a destination of size 257
 1078 |         sprintf(file_out_2, "tst_copy_%s", file_out);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bm_file.c:1079:33: warning: ‘sprintf’ may write a terminating nul past the end of the destination [-Wformat-overflow=]
 1079 |         sprintf(cmd, "cp %s %s\n", file_out, file_out_2);
      |                                 ^
bm_file.c:1079:9: note: ‘sprintf’ output between 6 and 518 bytes into a destination of size 517
 1079 |         sprintf(cmd, "cp %s %s\n", file_out, file_out_2);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
depbase=`echo tst_utils.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`;\