external/libassuan: Fix fallout of defining __STDC__ on Windows

...since 1bb0e17712 "Fix autoconf>=2.70
gcc-wrapper breakage", which had the side effect of preventing various
deprecated function declarations in system headers (e.g., isascii in addition to
__isascii).  This went unnoticed so far due to the traditionally lax handling of
missing function declarations in C, and only now started to cause

> conversion.c(94,9): error: call to undeclared function 'isascii'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>           if ((isascii (*istr) && isprint (*istr)) || (*istr >= 0x80))
>                ^

etc. with clang-cl 15 trunk after
<7d644e1215>
"[C11/C2x] Change the behavior of the implicit function declaration warning".

Where undeclared functions have been used in Windows-only code, they have been
replaced with their __STDC__-declared counterparts, and for occurrences in
shared code Windows-only macro definitions have been introduced (as would have
done in the system headers too, if __STDC__ was not defined) to not clutter the
shared code with #ifdefs.

Also, for getpid (resp. _getpid), the #include <process.h> was apparently
missing from the upstream code, even without our __STDC__ hack in
external/libassuan/ExternalProject_libassuan.mk (but never caused errors until
now, either).

Change-Id: I7442394d0c6e633bca1f6c7331d7ee51651179a4
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/133339
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

external/libassuan/UnpackedTarball_libassuan.mk

@@ -19,6 +19,7 @@ $(eval $(call gb_UnpackedTarball_add_patches,libassuan, \
     $(if $(filter MSC,$(COM)),external/libassuan/w32-build-fixes.patch.1) \
     external/libassuan/w32-build-fixes-2.patch \
     $(if $(filter LINUX,$(OS)),external/libassuan/rpath.patch) \
+    external/libassuan/w32-stdc.patch \
 ))
 
 # vim: set noet sw=4 ts=4:

external/libassuan/w32-stdc.patch

@@ -0,0 +1,74 @@
+--- src/assuan-handler.c
++++ src/assuan-handler.c
+@@ -938,7 +938,7 @@
+ #if defined(HAVE_W32CE_SYSTEM)
+         fdarray[n++] = (void*)fileno (ctx->outbound.data.fp);
+ #elif defined(HAVE_W32_SYSTEM)
+-        fdarray[n++] = (void*)_get_osfhandle (fileno (ctx->outbound.data.fp));
++        fdarray[n++] = (void*)_get_osfhandle (_fileno (ctx->outbound.data.fp));
+ #else
+         fdarray[n++] = fileno (ctx->outbound.data.fp);
+ #endif
+--- src/assuan-logging.c
++++ src/assuan-logging.c
+@@ -30,10 +30,15 @@
+ # ifdef HAVE_WINSOCK2_H
+ #  include <winsock2.h>
+ # endif
++# include <process.h>
++# define getpid _getpid
+ # include <windows.h>
+ #endif /*HAVE_W32_SYSTEM*/
+ #include <errno.h>
+ #include <ctype.h>
++#if defined HAVE_W32_SYSTEM
++#define isascii __isascii
++#endif
+ 
+ #include "assuan-defs.h"
+ 
+--- src/assuan-pipe-connect.c
++++ src/assuan-pipe-connect.c
+@@ -47,6 +47,8 @@
+ # ifdef HAVE_WINSOCK2_H
+ #  include <winsock2.h>
+ # endif
++# include <process.h>
++# define getpid _getpid
+ # include <windows.h>
+ #endif
+ 
+--- src/assuan-socket.c
++++ src/assuan-socket.c
+@@ -27,6 +27,8 @@
+ #include <stdlib.h>
+ #ifdef HAVE_W32_SYSTEM
+ # define WIN32_LEAN_AND_MEAN
++# include <process.h>
++# define getpid _getpid
+ # include <windows.h>
+ # include <wincrypt.h>
+ #ifndef HAVE_W32CE_SYSTEM
+--- src/conversion.c
++++ src/conversion.c
+@@ -27,6 +27,9 @@
+ #include <string.h>
+ #include <errno.h>
+ #include <ctype.h>
++#if defined HAVE_W32_SYSTEM
++#define isascii __isascii
++#endif
+ 
+ #include "assuan-defs.h"
+ #include "debug.h"
+--- src/system-w32.c
++++ src/system-w32.c
+@@ -453,7 +453,7 @@
+ 
+   /* Dup stderr to /dev/null unless it is in the list of FDs to be
+      passed to the child. */
+-  fd = assuan_fd_from_posix_fd (fileno (stderr));
++  fd = assuan_fd_from_posix_fd (_fileno (stderr));
+   fdp = fd_child_list;
+   if (fdp)
+     {