gitignore: ignore autoreconf-generated backup files

configure~ and src/config.h.in~ get regenerated by autoconf/autoheader
on every reconfigure and shouldn't be tracked.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: galastar

.gitignore

@@ -12,6 +12,8 @@
 *_opts.h
 .libs
 docs/web/
+configure~
+src/config.h.in~
 
 # Packages #
 ############