update .gitignore

with generic Autotools entries and a specific one for a generated
header. This allows building the project in the same directory as the
source.

.gitignore

@@ -3,3 +3,28 @@
 *.lo
 *.a
 *.la
+backtrace-supported.h
+
+# autotools
+Makefile
+Makefile.in
+/autom4te.cache
+/aclocal.m4
+/compile
+/configure
+/depcomp
+/install-sh
+/missing
+/stamp-h1
+/config.*
+/libtool
+/ltmain.sh
+/test-driver
+/test-suite.log
+.libs
+.deps
+.dirstamp
+*.log
+*.trs
+*.tar.gz
+