Do not compile/link snprintf.o if it is not needed

Makefile.am

@@ -52,7 +52,6 @@ libstrophe_la_SOURCES = \
 	src/sha1.c \
 	src/sha256.c \
 	src/sha512.c \
-	src/snprintf.c \
 	src/sock.c \
 	src/stanza.c \
 	src/tls.c \
@@ -76,6 +75,10 @@ libstrophe_la_SOURCES += \
 	src/tls.h \
 	src/util.h
 
+if NEED_SNPRINTF
+libstrophe_la_SOURCES += src/snprintf.c
+endif
+
 if DISABLE_TLS
 libstrophe_la_SOURCES += src/tls_dummy.c
 else

configure.ac

@@ -75,7 +75,7 @@ else
 fi
 
 AC_SEARCH_LIBS([socket], [network socket])
-AC_CHECK_FUNCS([snprintf vsnprintf])
+AC_CHECK_FUNCS([snprintf vsnprintf], [], [have_snprintf=no])
 AC_CHECK_DECLS([va_copy], [], [], [#include <stdarg.h>])
 
 if test "x$enable_tls" != xno -a "x$with_gnutls" == xyes; then
@@ -207,6 +207,7 @@ m4_ifdef([PKG_INSTALLDIR], [PKG_INSTALLDIR],
 
 AM_CONDITIONAL([PARSER_EXPAT], [test x$with_parser != xlibxml2])
 AM_CONDITIONAL([DISABLE_TLS], [test x$enable_tls = xno])
+AM_CONDITIONAL([NEED_SNPRINTF], [test x$have_snprintf = xno])
 AM_CONDITIONAL([TLS_WITH_GNUTLS], [test x$with_gnutls = xyes])
 
 # define while compiling