Pass new "compat includes" path via AC_SUBST.

This fixes the build when the directory path containing a space.
Found by Sevan Janiyan, tested by Job Snijders.  This doesn't fix
"make tests", however that is a different, pre-existing problem
that needs to be addressed separately.

Author: daztucker

Makefile.in

@@ -33,6 +33,7 @@ STRIP_OPT=@STRIP_OPT@
 TEST_SHELL=@TEST_SHELL@
 BUILDDIR=@abs_top_builddir@
 SK_STANDALONE=@SK_STANDALONE@
+COMPATINCLUDES="$(BUILDDIR)/@COMPATINCLUDES@"
 
 PATHS= -DSSHDIR=\"$(sysconfdir)\" \
 	-D_PATH_SSH_PROGRAM=\"$(SSH_PROGRAM)\" \
@@ -50,7 +51,7 @@ CC=@CC@
 LD=@LD@
 CFLAGS=@CFLAGS@
 CFLAGS_NOPIE=@CFLAGS_NOPIE@
-CPPFLAGS=-I. -I$(srcdir) @CPPFLAGS@ $(PATHS) @DEFS@
+CPPFLAGS=-I. -I$(srcdir) -I$(COMPATINCLUDES) @CPPFLAGS@ $(PATHS) @DEFS@
 PICFLAG=@PICFLAG@
 LIBS=@LIBS@
 CHANNELLIBS=@CHANNELLIBS@

configure.ac

@@ -526,7 +526,7 @@ AC_CHECK_HEADERS([ \
 # platform.  Usually these are just empty, but in some cases they'll include
 # the equivalent file.  This avoids having to wrap those includes in
 # '#ifdef HAVE_FOO_H'.  If we create any such headers, add the path to includes.
-compatincludes=no
+COMPATINCLUDES=""
 AC_CHECK_HEADERS([ \
     endian.h \
     ifaddrs.h \
@@ -541,8 +541,8 @@ AC_CHECK_HEADERS([ \
     sys/un.h \
     time.h \
     util.h], [], [
-	compatincludes="`pwd`/openbsd-compat/include"
-	header="$compatincludes/$ac_header"
+	COMPATINCLUDES="openbsd-compat/include"
+	header="$COMPATINCLUDES/$ac_header"
 	dir=`dirname "$header"`
 	mkdir -p "$dir"
 	case "$ac_header" in
@@ -552,9 +552,7 @@ AC_CHECK_HEADERS([ \
 	*)      ;;
 	esac >"$header"
 ])
-if test "$compatincludes" != "no"; then
-    CPPFLAGS="$CPPFLAGS -I$compatincludes"
-fi
+AC_SUBST([COMPATINCLUDES])
 
 AC_CHECK_DECLS([le32toh, le64toh, htole64], [], [], [
 #ifdef HAVE_SYS_TYPES_H