Integrate top-level .gitignore into .gitignore for each subdirectory

In preparation for the repository split, move the relevant contents of the
top-level .gitignore into the .gitignore for each immediate subdirectory.

.gitignore

@@ -1 +1,31 @@
 xcb_util_intro
+aclocal.m4
+autom4te.cache
+compile
+depcomp
+install-sh
+libtool
+ltmain.sh
+missing
+mkinstalldirs
+config.guess
+config.h
+config.h.in
+config.log
+config.status
+config.sub
+configure
+configure.lineno
+.deps
+.dirstamp
+.libs
+*.lo
+*.loT
+*.la
+Makefile
+Makefile.in
+stamp-h1
+*.o
+*.pc
+*.tar.bz2
+*.tar.gz