Windows: Implement os_setenv() using _putenv_s()

Windows does not have setenv(), instead the _putenv_s() function is used - added
a function check and fatal errors. Implemented os_setenv() for Windows.

Vim supports the original putenv() function if no alternative is available.
Neovim only supports systems where safer alternatives exist, so the check for
putenv() was removed from config/CMakeLists.txt.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/nvim/os/env.c b/src/nvim/os/env.c
index 0e052ced55..a791dca39c 100644
--- a/src/nvim/os/env.c
+++ b/src/nvim/os/env.c
@@ -46,7 +46,19 @@ bool os_env_exists(const char *name)
 int os_setenv(const char *name, const char *value, int overwrite)
   FUNC_ATTR_NONNULL_ALL
 {
+#ifdef HAVE_SETENV
   return setenv(name, value, overwrite);
+#elif defined(HAVE_PUTENV_S)
+  if (!overwrite && os_getenv(name) != NULL) {
+    return 0;
+  }
+  if (_putenv_s(name, value) == 0) {
+    return 0;
+  }
+  return -1;
+#else
+# error "This system has no implementation available for os_setenv()"
+#endif
 }
 
 /// Unset environment variable