Configuration should report incompatible gcc versions

[jjwilke]

GCC < 4.8.5 will accept the -std=c++11 flag, confusing the configure into thinking the compiler supports all of C++11. Previous versions of gcc support only a subset.

Configure happily finishes, but the code fails to compile with errors like:

In file included from ../../../src/sst/core/activity.h:19:0,
                 from main.cc:30:
../../../src/sst/core/serialization/serializable.h:227:11: error: expected ';' at end of member declaration
../../../src/sst/core/serialization/serializable.h:227:17: error: 'override' does not name a type

I'm not sure what the current auto configuration of C++11 flags is. If not too difficult to check for gcc and version number, better to have configuration directly complain about an incompatible gcc than to get bizarre compiler errors later.