configure: Place auxiliary files in own dir

.gitignore

@@ -7,31 +7,19 @@ Makefile
 Makefile.in
 aclocal.m4
 autom4te.cache/
-compile
-ar-lib
+/build-aux/
 confdefs.h
 conftest
 conftest.c
 conftest.err
-config.guess
-config.h.in
-config.h.in~
-config.h
-config.log
-config.status
-config.sub
+config.*
 config-win32.h
 configure
 configure.tmp
-depcomp
 doxygen*.tmp
 html/
-install-sh
-intl/
 libtool
-ltmain.sh
 m4/
-missing
 plugins/perl/irc.pm.h
 plugins/perl/xchat.pm.h
 plugins/perl/hexchat.pm.h