Fix a c++14 mingw compiler error and some warnings

[rtownson]

Fix a compiler error and some warnings found when compiling with mingw on windows, gcc 13.2.0. Note that currently users need to add -std=c++14 manually by editing the g++ settings in the installer, when installing with modern compilers that default to a newer standard. This should get resolved automatically at the next release when the installer is updated to include c++14 by default.

[mchamberland]

I've been struggling with installing on Windows these past two weeks. Will give that a shot!

[mchamberland]

It looks like inputting the -std=c++14 option in the 'Standard options' text field of the g++ settings in the configure Windows application gets ignored. I had to put it under the 'Optimization options' for it to get picked up. Is that a bug?

[rtownson]

It looks like inputting the -std=c++14 option in the 'Standard options' text field of the g++ settings in the configure Windows application gets ignored. I had to put it under the 'Optimization options' for it to get picked up. Is that a bug?

Sounds like a bug!

[mchamberland]

I don't really understand all of the egs_configure code, but I don't see where the standard g++ options get used. I can see the optimization options getting used in the create_egspp_config(), though.

[mchamberland]

Also, this PR appears to work as advertised: I was able to compile on Windows with mingw, gcc13.2.