First off, this doesn't cost us anything, because std::pair is defined
in <utility>, which qglobal.h unconditionally includes in C++ TUs.
More importantly, it prevents ODR violations: when a TU includes only
qtypeinfo.h, it will find std::pair<int, int> to be of Q_COMPLEX_TYPE,
in constrast with a TU which includes qpair.h, which will find it to
be of Q_PRIMITIVE_TYPE instead.
[ChangeLog][QtCore][QTypeInfo] The QTypeInfo for std::pair/QPair will
now be correct even if qpair.h hasn't been included, fixing an
One-Definition-Rule (ODR) violation.
Pick-to: 6.5 6.4 6.2
Change-Id: I51f579c123183af25aac9f0ffcf077f752848fb1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
f6b026eed1