windows.cfg: Fix wrong FlushConsoleInputBuffer configuration (#5526)

After flushing, the function returns. Before it was configured to
not-return.
A proper regression test was added.

Author: orbitcowboy

cfg/windows.cfg

@@ -4791,7 +4791,7 @@ HFONT CreateFont(
   </function>
   <!--BOOL WINAPI FlushConsoleInputBuffer(_In_ HANDLE hConsoleInput);-->
   <function name="FlushConsoleInputBuffer">
-    <noreturn>true</noreturn>
+    <noreturn>false</noreturn>
     <returnValue type="BOOL"/>
     <leak-ignore/>
     <arg nr="1" direction="in">

test/cfg/windows.cpp

@@ -7,7 +7,8 @@
 // No warnings about bad library configuration, unmatched suppressions, etc. exitcode=0
 //
 
-#include <windows.h>
+#include <Windows.h>
+#include <WinCon.h>
 #include <cstdio>
 #include <direct.h>
 #include <cstdlib>
@@ -18,6 +19,15 @@
 #include <atlstr.h>
 #include <string>
 
+/// https://learn.microsoft.com/en-us/windows/console/flushconsoleinputbuffer
+BOOL unreachableCode_FlushConsoleInputBuffer(int &val)
+{
+    const BOOL retVal = FlushConsoleInputBuffer(GetStdHandle(STD_INPUT_HANDLE));
+    // still reachable after call FlushConsoleInputBuffer()
+    val = 42;
+    return retVal;
+}
+
 /// https://learn.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-getmodulefilenamew
 std::string constVariable_GetModuleFileName(void) {
     char path[42];