Some extensions may require additional Makefile or config.m4 code
that can't be created by PECL_Gen.
Makefile code can be added using a <makefile> tag within
<deps> section. The tag data is written to a Makefile.fragment
file and registered within config.m4.
Additions to config.m4 itself can be put into a <configm4> tag
within <deps>. You can control whether the code is put near
the beginning or the end of config.m4 using the position=top or
position=bottom attribute.