Index: configure.ac
===================================================================
--- configure.ac	(revision 16)
+++ configure.ac	(working copy)
@@ -19,8 +19,7 @@
   ],[],[
     use_legacy_api=false
     AC_DEFINE(DISPATCH_NO_LEGACY,,Define to compile out legacy API)
-  ]
-)
+  ])
 AM_CONDITIONAL(USE_LEGACY_API, $use_legacy_api)
 
 #
@@ -34,22 +33,20 @@
     [Use less portable pthread TSD optimizations for Mac OS X.])
   ],[
     AC_DEFINE(USE_APPLE_TSD_OPTIMIZATIONS,,Define to compile in tsd optimizations)
-  ],[]
-)
+  ],[])
 
 AC_ARG_WITH([apple-semaphore-optimizations],
   [AS_HELP_STRING([--with-apple-semaphore-optimizations],
     [Use less portable semaphore optimizations for Mac OS X.])
   ],[
     AC_DEFINE(USE_APPLE_SEMAPHORE_OPTIMIZATIONS,,Define to compile in semaphore optimizations)
-  ],[]
-)
+  ],[])
 
 AC_PROG_CC
 AC_PROG_INSTALL
 AC_PROG_LIBTOOL
 
-AM_INIT_AUTOMAKE(AC_PACKAGE_NAME, AC_PACKAGE_VERSION)
+AM_INIT_AUTOMAKE([foreign nostdinc])
 
 #
 # Find libraries we will need
@@ -59,8 +56,7 @@
     use_libpthread=true
   ],[
     use_libpthread=false
-  ]
-)
+  ])
 AM_CONDITIONAL(USE_LIBPTHREAD, $use_libpthread)
 
 #
@@ -96,6 +92,23 @@
   AC_DEFINE(HAVE_POSIX_SEM,,Define if POSIX semaphores implemented)
 ])
 
+if test "$GCC"="yes"; then
+   WARN_FLAGS="-Wall -Werror"
+   # If the user added -march flags, don't override them, otherwise
+   # set to i686 so that GCC will implement atomic builtins
+   case "$CC $CFLAGS $CPPFLAGS" in
+     *" -march="*) ;;
+     *)  case $host_cpu in
+           i?86)  EXTRA_FLAGS="-march=i686" ;;
+	   x86_64|amd64) EXTRA_FLAGS="something else?" ;;
+         esac ;;
+   esac
+else
+   AC_MSG_ERROR([GCC is currently required to build libdispatch])
+fi
+
+AC_SUBST(WARN_FLAGS)
+AC_SUBST(EXTRA_FLAGS)
 #
 # Generate Makefiles.
 #
Index: src/Makefile.am
===================================================================
--- src/Makefile.am	(revision 16)
+++ src/Makefile.am	(working copy)
@@ -15,16 +15,8 @@
 	source.c	\
 	time.c
 
-libdispatch_la_CFLAGS=-Wall -Werror
+AM_CFLAGS=$(WARN_FLAGS) $(EXTRA_FLAGS)
 
-#
-# This will need some refinement: gcc requires a minimum of -march=i486 on
-# x86 in order to implement built-in atomic operations.  But when should we
-# define this optional argument?  We need appropriate configure parts to make
-# this conditional.
-#
-libdispatch_la_CFLAGS+=-march=i686
-
 if USE_LEGACY_API
 libdispatch_la_SOURCES+=	\
 	legacy.c
@@ -34,10 +26,4 @@
 libdispatch_la_LIBADD=-lpthread
 endif
 
-#
-# This hack is needed because the default include line from automake will add
-# -I. to compiler commands.  That leads to the local semaphore.h overriding
-# the one in /usr/local on systems using POSIX semaphores.  We can remove
-# this hack once header files are moved to their own directory.
-#
-DEFAULT_INCLUDES = @am__isrc@ -I.. -I$(top_builddir)/config
+AM_CPPFLAGS = -I$(top_srcdir) -I$(top_builddir)/config