Use strict function prototypes #945

`-Wstrict-prototypes` warn if a function is declared or defined without
specifying the argument types.

This warning disallow function prototypes with empty parameter list.
In C, a function declared with an empty parameter list accepts an
arbitrary number of arguments when being called. This is for historic
reasons; originally, C functions didn't have prototypes, as C evolved
from B, a typeless language. When prototypes were added, the original
typeless declarations were left in the language for backwards
compatibility.
Instead we should provide `void` in argument list to state
that function doesn't have arguments.

Also this warning disallow declaring type of the parameters after the
parentheses because Neovim header generator produce no declarations for
old-stlyle prototypes: it expects to find `{` after prototype.

src/nvim/os/time.c

@@ -16,7 +16,7 @@ static uv_cond_t delay_cond;
 # include "os/time.c.generated.h"
 #endif
 /// Initializes the time module
-void time_init()
+void time_init(void)
 {
   uv_mutex_init(&delay_mutex);
   uv_cond_init(&delay_cond);