Give up on compiling exo_planet_c_api.cpp with MSVC /EHs-c-:

There was one trouble maker (all other jobs worked):

Visual Studio 15 2017:

```
cl : Command line warning D9025: overriding '/EHc' with '/EHc-' [C:\projects\pybind11\tests\exo_planet_c_api.vcxproj]
...
C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\include\xlocale(319): error C2220: warning treated as error - no 'object' file generated [C:\projects\pybind11\tests\exo_planet_c_api.vcxproj]
C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\include\xlocale(319): warning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc
```

tests/CMakeLists.txt

@@ -493,9 +493,7 @@ foreach(target ${test_targets})
   endif()
 
   if("${target}" STREQUAL "exo_planet_c_api")
-    if(MSVC)
-      target_compile_options(${target} PRIVATE /EHs-c-)
-    elseif(CMAKE_CXX_COMPILER_ID MATCHES "(GNU|Intel|Clang|NVHPC)")
+    if(CMAKE_CXX_COMPILER_ID MATCHES "(GNU|Intel|Clang|NVHPC)")
       target_compile_options(${target} PRIVATE -fno-exceptions)
     endif()
   endif()

tests/exo_planet_c_api.cpp

@@ -3,8 +3,8 @@
 // In production situations it is totally fine to build with
 // C++ Exception Handling enabled. However, here we want to ensure that
 // C++ Exception Handling is not required.
-#ifdef __EMSCRIPTEN__
-// Too much trouble making the required cmake changes.
+#if defined(_MSC_VER) || defined(__EMSCRIPTEN__)
+// Too much trouble making the required cmake changes (see PR #5375).
 #else
 #    ifdef __cpp_exceptions
 // https://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations#__cpp_exceptions