fix(Data/SQLParser): restore Windows unistd guard in flex_lexer.h #5377

The bison/flex regen in 01f7ec2 overwrote a POCO-local hand-patch
in the generated flex_lexer.h that wrapped the unistd.h include in a
Windows guard. MSVC has no unistd.h, so clang-cl Windows builds
fail with:

  flex_lexer.h(470): fatal error: 'unistd.h' file not found

Re-apply the same conditional, with a POCO-LOCAL comment so the next
person who regens the lexer knows it has to be re-applied. flex's
%option set in flex_lexer.l has no equivalent for this - nounistd
would drop the include on every platform but flex's emitted runtime
calls (read/write/close/isatty) need either unistd.h or io.h, so the
conditional has to live in the generated header.

Author: aleks-f

Data/SQLParser/src/parser/flex_lexer.h

@@ -467,8 +467,17 @@ void yyfree ( void * , yyscan_t yyscanner );
  * down here because we want the user's section 1 to have been scanned first.
  * The user has a chance to override it with an option.
  */
+/* POCO-LOCAL: io.h provides the POSIX-ish I/O declarations flex's runtime
+ * uses (read/write/isatty/close) on MSVC; unistd.h does not exist there.
+ * Re-apply this conditional after every flex regen - it lives in the
+ * generated header, not in flex_lexer.l.
+ */
+#if defined(_WIN32) || defined(_WIN64)
+	#include <io.h>
+#else
 #include <unistd.h>
 #endif
+#endif
 
 #ifndef YY_EXTRA_TYPE
 #define YY_EXTRA_TYPE void *