Git: ignore autogen, doxygen and gdb config files

Adds some additional files to .gitignore.

Change-Id: Ia5af298a91919fe00392282c0e5bb88fa2811a52
Reviewed-on: https://gerrit.libreoffice.org/8437Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

.gitignore

@@ -33,6 +33,8 @@
 /aclocal.m4
 /autom4te.cache
 /autogen.input
+/autogen.lastrun
+/autogen.lastrun.bak
 /ChangeLog
 /config.Build.log
 /config.guess
@@ -95,3 +97,9 @@ xcuserdata
 *.v11*
 *.vcxproj*
 *.opensdf
+
+# doxygen output
+/docs
+
+# gdb config
+/.gdbinit