Merge #5954

5954: Use CMake to configure static C stdlib on Windows r=def- a=heinrich5991

Previously warnings were generated because we were passing /MTd-like arguments twice, due to us and CMake 3.15+ adding these arguments: https://cmake.org/cmake/help/v3.25/policy/CMP0091.html.

This requires CMake 3.15 on Windows.

This fixes #5940.

## Checklist

- [x] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test (especially base/) or added coverage to integration test
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: heinrich5991 <heinrich5991@gmail.com>

CMakeLists.txt

@@ -800,10 +800,11 @@ if(NOT(GTEST_FOUND) AND DOWNLOAD_GTEST)
 
       if(MSVC)
         foreach(target gtest gmock)
+          set_property(TARGET ${target} PROPERTY MSVC_RUNTIME_LIBRARY MultiThreaded$<${DBG}:Debug>)
           # `/w` disables all warnings. This is needed because `gtest` enables
           # `/WX` (equivalent of `-Werror`) for some reason, breaking builds
           # when MSVS adds new warnings.
-          target_compile_options(${target} PRIVATE $<$<NOT:${DBG}>:/MT> $<${DBG}:/MTd> /w)
+          target_compile_options(${target} PRIVATE /w)
         endforeach()
       endif()
 
@@ -2996,7 +2997,7 @@ set(TARGETS ${TARGETS_OWN} ${TARGETS_DEP})
 
 foreach(target ${TARGETS})
   if(MSVC)
-    target_compile_options(${target} PRIVATE $<$<NOT:${DBG}>:/MT> $<${DBG}:/MTd>) # Use static CRT
+    set_property(TARGET ${target} PROPERTY MSVC_RUNTIME_LIBRARY MultiThreaded$<${DBG}:Debug>) # Use static CRT
     target_compile_options(${target} PRIVATE /MP) # Use multiple cores
     target_compile_options(${target} PRIVATE /EHsc) # Only catch C++ exceptions with catch.
     target_compile_options(${target} PRIVATE /GS) # Protect the stack pointer.