Detect if sed supports --in-place

Not all versions of sed have the --in-place flag. Detect support for
the flag during ./configure and provide a fallback mechanism for those
systems where sed's behavior differs. The autoconf variable
${ac_inplace} can be used to choose the correct flags for editing a
file in place with sed.

Replace violating usages in Makefile.am with ${ac_inplace}.

Reviewed-by: Chris Dunlop <chris@onthe.net.au>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@ixsystems.com>
Closes #9463

config/always-sed.m4

@@ -0,0 +1,16 @@
+dnl #
+dnl # Set the flags used for sed in-place edits.
+dnl #
+AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_SED], [
+	ac_inplace=""
+	AC_CACHE_CHECK([for sed --in-place], [ac_cv_path_SED],
+		[AC_PATH_PROGS_FEATURE_CHECK([SED], [sed],
+			[[tmpfile=$(mktemp)
+			  echo foo > $tmpfile
+			  $ac_path_SED --in-place 's#foo#bar#' $tmpfile \
+			  && ac_cv_path_SED=$ac_path_SED
+			  rm $tmpfile]],
+			[ac_inplace="-i ''"])])
+	AS_IF([test "x$ac_inplace" = "x"], [ac_inplace="--in-place"])
+	AC_SUBST([ac_inplace])
+])

config/zfs-build.m4

@@ -164,6 +164,7 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS], [
 	ZFS_AC_CONFIG_ALWAYS_ARCH
 	ZFS_AC_CONFIG_ALWAYS_PYTHON
 	ZFS_AC_CONFIG_ALWAYS_PYZFS
+	ZFS_AC_CONFIG_ALWAYS_SED
 ])
 
 AC_DEFUN([ZFS_AC_CONFIG], [