git master should use gnulib module snprintf

[Ralf Wildenhues]

Hi Eric,

git master M4 uses snprintf in m4/output.c but does not use the snprintf
module from gnulib.  This leads to a link error on Tru64/OSF1:

autom4te_perllibdir='../../autoconf'/lib                                        
AUTOM4TE_CFG='../lib/autom4te.cfg'         ../bin/autom4te       -B '..'/lib -B 
'../../autoconf'/lib         --language=autotest -I . -I ../../autoconf/tests 
../../autoconf/tests/suite.at -o ./testsuite.tmp
15433:/home/rwild/local/alphaev5-dec-osf4.0d/bin/m4: /sbin/loader: Fatal Error: 
Unresolved symbol in /home/rwild/local/alphaev5-dec-osf4.0d/lib/libm4.so.0: 
snprintf
autom4te: /home/rwild/local/alphaev5-dec-osf4.0d/bin/m4 failed with exit 
status: 1

Cheers,
Ralf