refactor(windows)!: only support UCRT, even for mingw

The newer UCRT runtime has native support for UTF-8, including forcing
it as the active codepage even before `main()` is called. This means
the c runtime will properly convert windows WCHAR:s into UTF-8 bytes,
as early as the argv/argc params to `main()` . Whereas MSVCRT does not
support this reliably and required us to use `wmain()`.

Only MSVC supports using manifest files directly as source files.
The solution for other Windows toolchains is to use a .rc file.

runtime/doc/news.txt

@@ -45,6 +45,10 @@ API
 • Renamed `nvim__id_dictionary` (unsupported/experimental API) to
   `nvim__id_dict`.
 
+BUILD
+
+On Windows, only building with the UCRT runtime is supported.
+
 DEFAULTS
 
 • |]d-default| and |[d-default| accept a count.

src/nvim/CMakeLists.txt

@@ -120,8 +120,8 @@ elseif(MINGW)
   # Use POSIX compatible stdio in Mingw
   target_compile_definitions(main_lib INTERFACE __USE_MINGW_ANSI_STDIO)
 
-  # Enable wmain
-  target_link_libraries(nvim_bin PRIVATE -municode)
+  # wrapper for nvim.manifest
+  target_sources(main_lib INTERFACE ${CMAKE_CURRENT_LIST_DIR}/os/nvim.rc)
 elseif(CMAKE_C_COMPILER_ID STREQUAL "GNU")
   target_compile_options(main_lib INTERFACE
     -Wno-conversion

src/nvim/main.c

@@ -111,6 +111,9 @@
 
 #ifdef MSWIN
 # include "nvim/os/os_win_console.h"
+# ifndef _UCRT
+#  error UCRT is the only supported C runtime on windows
+# endif
 #endif
 
 #if defined(MSWIN) && !defined(MAKE_LIB)
@@ -241,22 +244,10 @@ void early_init(mparm_T *paramp)
 #ifdef MAKE_LIB
 int nvim_main(int argc, char **argv);  // silence -Wmissing-prototypes
 int nvim_main(int argc, char **argv)
-#elif defined(MSWIN)
-int wmain(int argc, wchar_t **argv_w)  // multibyte args on Windows. #7060
 #else
 int main(int argc, char **argv)
 #endif
 {
-#if defined(MSWIN) && !defined(MAKE_LIB)
-  char **argv = xmalloc((size_t)argc * sizeof(char *));
-  for (int i = 0; i < argc; i++) {
-    char *buf = NULL;
-    utf16_to_utf8(argv_w[i], -1, &buf);
-    assert(buf);
-    argv[i] = buf;
-  }
-#endif
-
   argv0 = argv[0];
 
   if (!appname_is_valid()) {

src/nvim/os/nvim.rc

@@ -0,0 +1,2 @@
+#include "winuser.h"
+2 RT_MANIFEST nvim.manifest

test/functional/fixtures/CMakeLists.txt

@@ -1,7 +1,4 @@
 add_library(test_lib INTERFACE)
-if(MINGW)
-  target_link_libraries(test_lib INTERFACE -municode)
-endif()
 if(WIN32)
   target_compile_definitions(test_lib INTERFACE MSWIN)
 endif()