s4-heimdal: Fix the format-truncation errors.

s4-heimdal: Fix the format-truncation errors.

../source4/heimdal/lib/com_err/compile_et.c: In function ‘generate_h’:
../source4/heimdal/lib/com_err/compile_et.c:138:33: error: ‘%s’ directive output may be truncated writing up to 127 bytes into a region of size 126 [-Werror=format-truncation=]
     snprintf(fn, sizeof(fn), "__%s__", hfn);
                                 ^~     ~~~
../source4/heimdal/lib/com_err/compile_et.c:138:5: note: ‘snprintf’ output between 5 and 132 bytes into a destination of size 128
     snprintf(fn, sizeof(fn), "__%s__", hfn);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../source4/heimdal/lib/com_err/compile_et.c: In function ‘main’:
../source4/heimdal/lib/com_err/compile_et.c:234:35: error: ‘.h’ directive output may be truncated writing 2 bytes into a region of size between 1 and 128 [-Werror=format-truncation=]
     snprintf(hfn, sizeof(hfn), "%s.h", Basename);
                                   ^~
../source4/heimdal/lib/com_err/compile_et.c:234:5: note: ‘snprintf’ output between 3 and 130 bytes into a destination of size 128
     snprintf(hfn, sizeof(hfn), "%s.h", Basename);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../source4/heimdal/lib/com_err/compile_et.c:235:35: error: ‘.c’ directive output may be truncated writing 2 bytes into a region of size between 1 and 128 [-Werror=format-truncation=]
     snprintf(cfn, sizeof(cfn), "%s.c", Basename);
                                   ^~
../source4/heimdal/lib/com_err/compile_et.c:235:5: note: ‘snprintf’ output between 3 and 130 bytes into a destination of size 128
     snprintf(cfn, sizeof(cfn), "%s.c", Basename);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13437

Guenther

Signed-off-by: Günther Deschner <gd@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Fri Jun  8 13:23:51 CEST 2018 on sn-devel-144