Everywhere: void arguments to C functions

Problem:
- C functions with no arguments require a single `void` in the argument list.

Solution:
- Put the `void` in the argument list of functions in C header files.

Base/usr/share/man/man2/geteuid.md

@@ -7,8 +7,8 @@ geteuid, getegid - get effective user / group id
 ```**c++
 #include <unistd.h>
 
-uid_t geteuid();
-gid_t getegid();
+uid_t geteuid(void);
+gid_t getegid(void);
 ```
 
 ## Description

Base/usr/share/man/man2/getuid.md

@@ -7,8 +7,8 @@ getuid, getgid - get real user / group id
 ```**c++
 #include <unistd.h>
 
-uid_t getuid();
-gid_t getgid();
+uid_t getuid(void);
+gid_t getgid(void);
 ```
 
 ## Description