._src_Makefile.am

bin_PROGRAMS = greetings
greetings_SOURCES = main.cpp greet.h
EXTRA_greetings_SOURCES = darwin/greeting.mm darwin/greet.cpp mingw32/greet.cpp
if OS_DARWIN
  greetings_CFLAGS = -framework -Xlinker Foundation
  greetings_SOURCES += darwin/greeting.mm darwin/greet.cpp
endif
if OS_MINGW32
  greetings_SOURCES += mingw32/greet.cpp
endif

configure.ac

AC_INIT([greetings], [1.0], [lee.hambley@gmail.com])

AC_CANONICAL_HOST
AC_PROG_CC
AC_PROG_CXX
AC_PROG_OBJC
AC_PROG_OBJCXX
AC_PROG_MAKE_SET

# http://www.gnu.org/software/hello/manual/automake/Suffixes.html#Suffixes
# SUFFIXES = .mm

# AC_CONFIG_AUX_DIR([./.aux])

case "$host_os" in 
  darwin*)
    os_module=darwin;;
  mingw32)
    os_module=mingw32;;
  *)
    AC_MSG_ERROR([What crazy OS is $host_os]);;
esac

AM_CONDITIONAL([OS_DARWIN],  [test $os_module = darwin])
AM_CONDITIONAL([OS_MINGW32], [test $os_module = mingw32])

AM_INIT_AUTOMAKE([-Wall foreign subdir-objects ])
AC_CONFIG_FILES([ Makefile src/Makefile ])
AC_OUTPUT

Makefile.am

SUBDIRS = src