[Bug preprocessor/69543] New: _Pragma does not apply within macro

["dmalcolm at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69543

            Bug ID: 69543
           Summary: _Pragma does not apply within macro
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
  Target Milestone: ---

https://gcc.gnu.org/ml/gcc-patches/2016-01/msg02243.html
reported a regression introduced by r232893 (for PR preprocessor/69126)

Minimal reproducer seems to be:
$ cat /tmp/test.c
# define YY_IGNORE_MAYBE_UNINITIALIZED_BEGIN \
    _Pragma ("GCC diagnostic push") \
    _Pragma ("GCC diagnostic ignored \"-Wuninitialized\"")\
    _Pragma ("GCC diagnostic ignored \"-Wmaybe-uninitialized\"")
# define YY_IGNORE_MAYBE_UNINITIALIZED_END \
    _Pragma ("GCC diagnostic pop")

void test (char yylval)
{
  char *yyvsp;
  YY_IGNORE_MAYBE_UNINITIALIZED_BEGIN
  *++yyvsp = yylval;
  YY_IGNORE_MAYBE_UNINITIALIZED_END
}

$ ./xgcc -B. -c /tmp/test.c -Wall
/tmp/test.c: In function 'test':
/tmp/test.c:12:12: warning: 'yyvsp' is used uninitialized in this
function [-Wuninitialized]
   *++yyvsp = yylval;
   ~~~~~~~~~^~~~~~~~

$ ./xgcc -B. -c /tmp/test.c -save-temps
$ ./xgcc -B. -c test.i -Wall
(compiles with no warnings)