build: use portable Makefile variables

* Makefile.am: use '$?' instead of '$<'
  $< in a non-inference rule is a GNU-make extension, which fails with
  BSD make.

(cherry picked from commit 243928da395080d7895111d5e5c0f1ff5f9e95fb)

diff --git a/Makefile.am b/Makefile.am
index 24d1730..1c14948 100644 (file)
--- a/Makefile.am
+++ b/Makefile.am
@@ -32,9 +32,9 @@ man_MANS = virt-what.1
 
 virt-what.1: virt-what.pod
        pod2man -c "Virtualization Support" --release "$(PACKAGE)-$(VERSION)" \
-         $< > $@
+         $? > $@
 virt-what.txt: virt-what.pod
-       pod2text $< > $@
+       pod2text $? > $@
 
 endif