cmake: allow CURL_STATIC_CRT with UCRT VS2015+ builds

After this patch, we're back to 8.12.1, but disallowing
`CURL_STATIC_CRT=ON` with shared curl exe built with VS2013 or older.
Because those may crash. A stable reprducer is with `ENABLE_DEBUG=ON`
and calling `curl.exe -V`.

You can pass the necessary CMake and MSVC linker options manually,
to get around this condition.

Shared build with static UCRT may be crashing too, depending on
conditions. Consult the documentation about limitations of static CRT:
https://learn.microsoft.com/cpp/c-runtime-library/crt-library-features

Follow-up to 049352dd80 #16516
Follow-up to edfa537100 #16456
Ref: #16394
Closes #16522

docs/INSTALL-CMAKE.md

@@ -238,7 +238,7 @@ target_link_libraries(my_target PRIVATE CURL::libcurl)
 - `CURL_LIBCURL_VERSIONED_SYMBOLS`:         Enable libcurl versioned symbols. Default: `OFF`
 - `CURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX`:  Override default versioned symbol prefix. Default: `<TLS-BACKEND>_` or `MULTISSL_`
 - `CURL_LTO`:                               Enable compiler Link Time Optimizations. Default: `OFF`
-- `CURL_STATIC_CRT`:                        Build libcurl with static CRT with MSVC (`/MT`) (requires static or no curl executable). Default: `OFF`
+- `CURL_STATIC_CRT`:                        Build libcurl with static CRT with MSVC (`/MT`) (requires UCRT, static libcurl or no curl executable). Default: `OFF`
 - `CURL_TARGET_WINDOWS_VERSION`:            Minimum target Windows version as hex string.
 - `CURL_TEST_BUNDLES`:                      Bundle `libtest` and `unittest` tests into single binaries. Default: `OFF`
 - `CURL_WERROR`:                            Turn compiler warnings into errors. Default: `OFF`