Fix multiple problems when compiling with LLVM/Windows (clang-cl)

Fix multiple problems when compiling with LLVM/Windows (clang-cl)

When using the LLVM clang compiler instead the MSVC cl.exe but with
the same build environment as MSVC, clang encounters a few errors:

src\openvpn\socket.c(3550,23): warning: assigning to 'CHAR *' (aka 'char
*') from 'uint8_t *' (aka 'unsigned char *') converts between pointers to
integer types with different sign [-Wpointer-sign]
        wsabuf[0].buf = BPTR(&sock->reads.buf);
                      ^ ~~~~~~~~~~~~~~~~~~~~~~
src\openvpn\socket.c(3670,23): warning: assigning to 'CHAR *' (aka 'char
*') from 'uint8_t *' (aka 'unsigned char *') converts between pointers to
integer types with different sign [-Wpointer-sign]
        wsabuf[0].buf = BPTR(&sock->writes.buf);
                      ^ ~~~~~~~~~~~~~~~~~~~~~~~

Use BSTR instead of BPTR, which casts to the correct type that is
expected.

src\compat\compat-gettimeofday.c(105,18): error: assignment to cast is
illegal, lvalue casts are not supported
    tv->tv_sec = (long)last_sec = (long)sec;

Split into two assignments to avoid the illegal cast

include\stdint.h(18,28): error: typedef redefinition with different types
('signed char' vs 'char')
typedef signed char        int8_t;
                           ^
openvpn\config-msvc.h(162,16): note: previous definition is here
typedef __int8 int8_t;

Removes our custom int type typdefs from config-msvc.h and replace it
with an include of inttypes.h.

C:\Program Files (x86)\Windows
Kits\10\include\10.0.19041.0\shared\tcpmib.h(56,3): error: typedef
redefinition with different types ('enum MIB_TCP_STATE' vs 'int')
} MIB_TCP_STATE;
  ^
C:\Users\User\source\repos\openvpn\src\openvpn/syshead.h(369,13): note:
previous definition is here
typedef int MIB_TCP_STATE;
            ^
1 error generated.

This seems to be for mingw32 only, so guard this with a mingw32
compiler guard.

\src\openvpn\tun.c(3727,34): warning: passing 'char [256]' to parameter of
type 'LPBYTE' (aka 'unsigned char *') converts between pointers to integer
types with different sign [-Wpointer-sign]
                                 net_cfg_instance_id,
                                 ^~~~~~~~~~~~~~~~~~~
C:\Program Files (x86)\Windows
Kits\10\include\10.0.19041.0\um\winreg.h(955,88): note: passing argument
to parameter 'lpData' here

This is windows specific code, use the Windows LPBTYE in the
definitions. (long pointer to BYTE (long pointer as far/near pointer
relict from windows 16 bit times, in moddern words (unsigned char *))

Fix also a few other char vs uint8/unisgned char/BYTE issues in tun.c

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20210319114631.20459-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg21719.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>