QQmlTrace: getpid() requires unistd.h
QQmlTrace: getpid() requires unistd.h

Doesn't build on MacOS if you omit this include and uncomment
define QML_ENABLE_TRACE in qqmltrace_p.h

Change-Id: I78ed43b16a006699449202dd234e43be2f7b84fd
Reviewed-by: Alan Alpert <da25f2afbbb946022229108d81aeba0c6b35c5c3@blackberry.com>

qmlc/qtdeclarative,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,corngood/qtdeclarative,corngood/qtdeclarative,qmlc/qtdeclarative,matthewvogt/qtdeclarative,matthewvogt/qtdeclarative,matthewvogt/qtdeclarative,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,corngood/qtdeclarative,matthewvogt/qtdeclarative,mgrunditz/qtdeclarative-2d,corngood/qtdeclarative,matthewvogt/qtdeclarative,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,matthewvogt/qtdeclarative,matthewvogt/qtdeclarative,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,corngood/qtdeclarative,matthewvogt/qtdeclarative,corngood/qtdeclarative,corngood/qtdeclarative,mgrunditz/qtdeclarative-2d