Enable /Zc:throwingNew when building with MSVC

[jjuhl]

From Microsoft's documentation
(https://learn.microsoft.com/en-us/cpp/build/reference/zc-throwingnew-assume-operator-new-throws?view=msvc-170) :

"When the /Zc:throwingNew option is specified, the compiler optimizes calls to operator new to skip checks for a null pointer return. This option tells the compiler to assume that all linked implementations of operator new and custom allocators conform to the C++ standard and throw on allocation failure. By default in Visual Studio, the compiler pessimistically generates null checks (/Zc:throwingNew-) for these calls, because users can link with a non-throwing implementation of operator new or write custom allocator routines that return null pointers."

Nothing in TGUI assumes that new returns nullptr on failure and if any users write an allocator that does so or explicitly link to a non-conforming, non-throwing allocator, then they are advanced enough to know to locally disable this option. We should not penalize the common user to cater to an obscure corner case (and this also better matches behaviour with other compilers). Let's default to the standard compliant, and better performing, behaviour.

[jjuhl]

Need to check for clang. Never mind for now. I'll get back to this at some point in the future.

[texus]

I've added a section for MSVC-specific compiler flags now.
It's best to keep the MSVC and Clang-CL flags the same were possible, but in edge cases like this you can now specify it separately.

Clang-CL already assumes the new implementation is conform, so it doesn't have the option.

This has been committed in b462ae8 and 2c23d2a