Suppress clang dynamic exception specifiers warning

Can't really remove the dynamic exception specifiers
and still be compatible with the superclass in C++98,
so just suppress the warning with a pragma.

Change-Id: I04ed166ad4111fd8e7401b6753f29749dde87f77
Merge topic 'dyn-excp-spec-in-utf8' into master

e58852e9 Suppress clang dynamic exception specifiers warning