Switch all targets to clang/C++11.

Issue: PLCR-538
C++11 fix: An explicit instantiation must be declared within the template's namespace.

Issue: PLCR-538
C++11 fix: Avoid casting the SIG_* function-types to (in theory) constant uintptr_t values.

Clang complains about the use of SIG_DFL/SIG_IGN in a switch case; while
they are implemented as integer constants cast to function pointers,

Our casting them back for use in a switch() statement is not strictly
well-defined, so I've switched them to the more correct if () statements.

Issue: PLCR-538
C++11 fix: Add explicit static casts for cases where were relying on implicit conversion to a narrower/signed/unsigned integral type.

Issue: PLCR-538
Merge pull request #4 in PLCR/plcrashreporter from feature/PLCR-538-switch-to-cpp11 to master

* commit '2b3b33a4d346c84fd8653e1e9e002cdd281e4a6e':
  C++11 fix: Add explicit static casts for cases where were relying on implicit conversion to a narrower/signed/unsigned integral type.
  C++11 fix: Avoid casting the SIG_* function-types to (in theory) constant uintptr_t values.
  C++11 fix: An explicit instantiation must be declared within the template's namespace.
  Switch all targets to clang/C++11.