[OE-core] [PATCH] boost: Convert ??= weaker assingment to weak ?= assignment

[Khem Raj]

??= does not react at all with
BOOST_LIBS += "${@base_contains('PACKAGECONFIG', 'python', 'python', '', d)}"

even though we have

PACKAGECONFIG ??= "" it does not honor it and always add python to
BOOST_LIBS but the dependency is not added so it fails to build
complaining for missing python headers which is a understood outcome

When converted to ?= it works as expected and only add --with-python
in bjam when python is specified in PACKAGECONFIG otherwise not.

Is it a bitbake bug ? in anycase ?= should be enough of loose rope
to let user/distro configure the packageconfig policy

Signed-off-by: Khem Raj <raj.khem at gmail.com>
---
 meta/recipes-support/boost/boost.inc |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meta/recipes-support/boost/boost.inc b/meta/recipes-support/boost/boost.inc
index f13051c..f0f9eb8 100644
--- a/meta/recipes-support/boost/boost.inc
+++ b/meta/recipes-support/boost/boost.inc
@@ -19,7 +19,7 @@ BOOST_LIBS = "\
 	"
 
 # optional boost-python library
-PACKAGECONFIG ??= ""
+PACKAGECONFIG ?= ""
 PACKAGECONFIG[python] = ",,python"
 BOOST_LIBS += "${@base_contains('PACKAGECONFIG', 'python', 'python', '', d)}"
 inherit python-dir
-- 
1.7.10.4