cmake build: missing /guard:ehcont compiler flag

[matbech]

Compared to the internal stl build (msbuild), the cmake build is missing the following compiler option for 64-bit builds: /guard:ehcont

To reproduce, use cmake to build the x64 target and then link to the .lib (shared dll). This results in the following warning:
msvcprt.lib(vector_algorithms.cpp.obj) : warning LNK4291: module may contain '__except' (Structured Exception Handling) but was not compiled with /guard:ehcont; generating conservative metadata

When linking to the msvcprt.lib library provided by Visual Studio, there is no warning.

[StephanTLavavej]

Yep, great catch. This is controlled by internal src/vctools/crt/crt_build.settings.targets (outside of the STL's sources which are mirrored in src/vctools/crt/github):

<!-- Compile all the libraries with /guard:ehcont option for amd64 architecture. VSO #1073832 -->
<GuardEhContMetadata>true</GuardEhContMetadata>

As the comment indicates, this was VSO-1073832 resolved by MSVC-PR-241996 merged on 2020-04-29, after we created the CMake build system for the STL in 2019, which is why we missed this.