[jhbuild] use proper if construction to avoid running rules when not in srcdir

[Frederic Peters <fpeters src gnome org>]

commit e493ce3ae67315e17980c5053f011e0c1fa00c28
Author: Frederic Peters <fpeters 0d be>
Date:   Wed Apr 29 09:53:21 2009 +0200

    use proper if construction to avoid running rules when not in srcdir
---
 Makefile.am |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/Makefile.am b/Makefile.am
index 441f9ba..97e898c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -26,11 +26,14 @@ DISTCLEANFILES = 		\
 # those won't be executed by make distcheck, it is necessary as they build
 # in source tree and do install to ~/bin/
 all-local:
-	test z"$(srcdir)" = z"." && $(MAKE) -f Makefile.plain || true
+	if [ z"$(srcdir)" = z"." ]; then \
+		$(MAKE) -f Makefile.plain; \
+	fi
 
 install-exec-local:
-	test z"$(srcdir)" = z"." && \
+	if [ z"$(srcdir)" = z"." ]; then \
 		$(MAKE) -f Makefile.plain install \
 			bindir="$(bindir)" \
-			datarootdir="$(datarootdir)"
+			datarootdir="$(datarootdir)"; \
+	fi