msvcrt: Implement bufsiz block flushing behavior.

dlls/msvcrt/file.c

@@ -3720,6 +3720,18 @@ MSVCRT_size_t CDECL MSVCRT_fwrite(const void *ptr, MSVCRT_size_t size, MSVCRT_si
             }
             written += wrcnt;
             wrcnt = 0;
+        } else if(file->_bufsiz && wrcnt >= file->_bufsiz) {
+            MSVCRT_size_t pcnt=(wrcnt / file->_bufsiz) * file->_bufsiz;
+            if(msvcrt_flush_buffer(file) == MSVCRT_EOF)
+                break;
+
+            if(MSVCRT__write(file->_file, ptr, pcnt) <= 0) {
+                file->_flag |= MSVCRT__IOERR;
+                break;
+            }
+            written += pcnt;
+            wrcnt -= pcnt;
+            ptr = (const char*)ptr + pcnt;
         } else {
             if(MSVCRT__flsbuf(*(const char*)ptr, file) == MSVCRT_EOF)
                 break;

dlls/msvcrt/tests/file.c

@@ -2243,7 +2243,7 @@ static void test_write_flush_size(FILE *file, int bufsize)
         fseek(file, 0, SEEK_SET);
         ok(fread(inbuffer, 1, bufsize, file) == bufsize, "read failed\n");
         if (size == bufsize)
-            todo_wine ok(memcmp(outbuffer, inbuffer, bufsize) == 0, "missing flush by %d byte write\n", size);
+            ok(memcmp(outbuffer, inbuffer, bufsize) == 0, "missing flush by %d byte write\n", size);
         else
             ok(memcmp(outbuffer, inbuffer, bufsize) != 0, "unexpected flush by %d byte write\n", size);
     }