Make some functions static in non-Microsoft builds.

Make some functions static in non-Microsoft builds.

On my platform (Fedora 19 x86-64), this shrinks the
Emacs executable (text+data) by 0.25%.
* dispextern.h (erase_phys_cursor) [!WINDOWSNT]:
(load_color) [!MSDOS]:
* gnutls.h (emacs_gnutls_transport_set_errno) [!WINDOWSNT]:
* keyboard.h (make_ctrl_char) [!WINDOWSNT]:
* lisp.h (check_existing):
* process.h (conv_sockaddr_to_lisp, network_interface_list)
(network_interface_info) [!WINDOWSNT]:
* termhooks.h (encode_terminal_code) [!WINDOWSNT]:
Remove extern decls.
* fileio.c (check_existing):
* keyboard.c (make_ctrl_char) [!WINDOWSNT]:
* process.c (conv_sockaddr_to_lisp, network_interface_list)
(network_interface_info) [!WINDOWSNT]:
* term.c (encode_terminal_code) [!WINDOWSNT]:
* xdisp.c (erase_phys_cursor) [!WINDOWSNT]:
* xfaces.c (load_color) [!MSDOS]:
Now static.
* fileio.c (check_existing, check_executable, check_writable):
* process.c (network_interface_list, network_interface_info):
Move earlier, so that we don't need forward decls.
* gnutls.c (fn_gnutls_transport_set_errno)
(emacs_gnutls_transport_set_errno) [!WINDOWNT]:
Remove; unused.
* w32.c (init_environment): Use faccessat rather than
check_existing, partly for consistency with the rest of the code
in this file, partly so that check_existing can be static.