Merging r182072:
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r182072 | rsmith | 2013-05-16 19:19:35 -0700 (Thu, 16 May 2013) | 6 lines

PR15757: When we instantiate an inheriting constructor template, also
instantiate the inherited constructor template and mark that as the constructor
which the instantiated specialization is inheriting. This fixes a
crash-on-valid when trying to compute the exception specification of a
specialization of the inheriting constructor.

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