Fix compile for libstdc++ with _GLIBCXX_DEBUG

9 jobs for prop-partial-specialisation in 3 minutes and 53 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #68954
VS2015
VS2015-32-bit

00:01:16

passed #68953
VS2015
VS2015-64-bit

00:01:18

passed #68952
VS2017
VS2017-32-bit

00:01:16

passed #68951
VS2015
VS2017-64-bit

00:01:18

passed #68948
Linux
clang-c++11

00:03:50

passed #68950
Linux
cppcheck

00:00:34

passed #68955
Linux
doc

00:00:18

passed #68947
Linux
gcc-c++11

00:03:53

passed #68949
Apple
macos-c++11

00:01:38