* srfi/srfi-37.scm.in: New file, taken from Guile 2.0.9.
* m4/guix.m4: New macro.
* configure.ac: Use it.  Define Automake conditional `INSTALL_SRFI_37'.
* Makefile.am (nobase_nodist_guilemodule_DATA)[INSTALL_SRFI_37]: Add
  srfi/srfi-37.scm.
  (GOBJECTS)[INSTALL_SRFI_37]: Add srfi/srfi-37.go.
  (srfi/srfi-37.scm)[INSTALL_SRFI_37]: New target.
  (EXTRA_DIST): Add srfi/srfi-37.scm.in.