fix centos6.6 docker build with overlay
diff --git a/tools/run_tests/artifact_targets.py b/tools/run_tests/artifact_targets.py
index 5d678a5..cf056ec 100644
--- a/tools/run_tests/artifact_targets.py
+++ b/tools/run_tests/artifact_targets.py
@@ -250,7 +250,7 @@
cxxflags = '-DNDEBUG %s' % _ARCH_FLAG_MAP[self.arch]
ldflags = '%s' % _ARCH_FLAG_MAP[self.arch]
if self.platform != 'macos':
- ldflags += ' -static-libgcc -static-libstdc++ -s'
+ ldflags += ' -static-libgcc -static-libstdc++ -s'
environ={'CONFIG': 'opt',
'CXXFLAGS': cxxflags,
'LDFLAGS': ldflags,