Opening a bug to track the underlying issue that caused me to submit this patch:
https://gcc.gnu.org/ml/gcc-patches/2017-05/msg00481.html
https://gcc.gnu.org/ml/gcc-patches/2017-03/msg01325.html

When compiling my fork of binutils-gdb, I get a lot of warnings like this one on one file:

unwind-ia64.c:183:30: warning: macro argument "code" would be stringified in traditional C
 #define UNW_DEC_BAD_CODE(code)   \
                              ^

To reduce it to a testcase, we can modify gcc.dg/pragma-diag-7.c to look like this:

$ cat pragma-diag-7.c
/* { dg-do compile } */

unsigned long ok = 0UL;
#pragma GCC diagnostic push
#pragma GCC diagnostic warning "-Wtraditional"
unsigned long bad = 1UL; /* { dg-warning "suffix" } */
/* Note the extra space before the pragma on this next line: */
 #pragma GCC diagnostic pop
unsigned long ok_again = 2UL; /* { dg-bogus "suffix" } */

/* Redundant with the previous pop, but just shows that it fails to stop the
 * following warning with an unpatched GCC: */
#pragma GCC diagnostic ignored "-Wtraditional"

/* { dg-bogus "would be stringified" .+1 } */
#define UNW_DEC_PROLOGUE(fmt, body, rlen, arg) \
  do {									\
      unw_rlen = rlen;							\
      *(int *)arg = body;						\
      printf("    %s:%s(rlen=%lu)\n",					\
             fmt, (body ? "body" : "prologue"), (unsigned long)rlen);	\
  } while (0)
$ /usr/local/bin/gcc -c pragma-diag-7.c
pragma-diag-7.c:6:21: warning: traditional C rejects the "UL" suffix [-Wtraditional]
 unsigned long bad = 1UL; /* { dg-warning "suffix" } */
                     ^~~
pragma-diag-7.c:16:46: warning: macro argument "rlen" would be stringified in traditional C
 #define UNW_DEC_PROLOGUE(fmt, body, rlen, arg) \
                                              ^
pragma-diag-7.c:16:46: warning: macro argument "body" would be stringified in traditional C
$ 

To get rid of the unwanted warnings, all that is necessary is a 1-line patch to libcpp/macro.c to change a call to cpp_error with CPP_DL_WARNING into a call to cpp_warning with CPP_W_TRADITIONAL instead. The patch is already linked above.