Add CMake option to toggle stack protection

[chrisdalke]

Using the MinGW-W64 compiler on Windows results in a segfault when a database is initially opened. This seems to be the result of the -fstack-protector flag, which has patchy support in MinGW.

Note some other major projects that have encountered this, and don't add this flag when compiling with MinGW on Windows:
bitcoin/bitcoin#8732
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86832

I can reproduce this with the example program and embedded sqlite3 library -- Building with MSVC works fine, and building with MinGW-W64 with the flag removed works fine, but segfaults at sqlite3_open_v2() with the flag added.

This PR adds a CMake option, SQLITECPP_USE_STACK_PROTECTION, defaulting to enabled, which allows disabling of this flag. Some other pull requests on this project to improve hardening (see #262) also mention this flag. In KOLANICH's PR, he excludes this flag unless the platform is Linux. I think that a good short-term solution short of refactoring all the hardening flags is to just keep this behind an option and document it with a comment in the CMakeFile.

[coveralls]

Coverage remained the same at 100.0% when pulling 1aa8286 on chrisdalke:master into f757b64 on SRombauts:master.

[SRombauts]

Thanks a lot, I'll also have a look at the aforementioned PR!

Cheers!
Sébastien