[gnome-sdk-images] Make sure we always clean RPB_BUILD_ROOT inside the sdk too

[Alexander Larsson <alexl src gnome org>]

commit 242f060aa0d9a1aa11988b1b88c2fec45e910339
Author: Alexander Larsson <alexl redhat com>
Date:   Wed Mar 25 16:43:45 2015 +0100

    Make sure we always clean RPB_BUILD_ROOT inside the sdk too

 packages/SOURCES/rpm-macros |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/packages/SOURCES/rpm-macros b/packages/SOURCES/rpm-macros
index 7066873..c5cbfea 100644
--- a/packages/SOURCES/rpm-macros
+++ b/packages/SOURCES/rpm-macros
@@ -31,3 +31,9 @@
 %install %{?_enable_debug_packages:%{?buildsubdir:%{debug_package}}}\
 %%install\
 %{nil}
+
+%__spec_install_pre %{___build_pre}\
+    [ "$RPM_BUILD_ROOT" != "/" ] && rm -rf "${RPM_BUILD_ROOT}"\
+    mkdir -p `dirname "$RPM_BUILD_ROOT"`\
+    mkdir "$RPM_BUILD_ROOT"\
+%{nil}