Fix testsuite build for GCC 7 -Wformat-truncation.

This patch fixes the glibc testsuite build for GCC 7
-Wformat-truncation, newly moved out of -Wformat-length and with some
further warnings that didn't previously appear.  Two tests that
previously disabled -Wformat-length are changed to disable
-Wformat-truncation instead; two others are made to disable that
option as well.

Tested (compilation only) with build-many-glibcs.py for aarch64 with
GCC mainline.

	* stdio-common/tst-printf.c [__GNUC_PREREQ (7, 0)]: Ignore
	-Wformat-truncation instead of -Wformat-length.
	* time/tst-strptime2.c (mkbuf) [__GNUC_PREREQ (7, 0)]: Likewise.
	* stdio-common/tstdiomisc.c (F): Ignore -Wformat-truncation for
	GCC 7.
	* wcsmbs/tst-wcstof.c: Include <libc-internal.h>.
	(do_test): Ignore -Wformat-truncation for GCC 7.

1 files changed, 8 insertions, 0 deletions

diff --git a/wcsmbs/tst-wcstof.c b/wcsmbs/tst-wcstof.c
index 576a58c023..861f65905a 100644
--- a/wcsmbs/tst-wcstof.c
+++ b/wcsmbs/tst-wcstof.c
@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <wctype.h>
+#include <libc-internal.h>
 
 static int
 do_test (void)
@@ -14,7 +15,14 @@ do_test (void)
   tmp[1] = '1';
   tmp[2] = 0;
 
+  /* GCC does not know the result of wcstof so cannot see that the
+     snprintf output is not truncated.  */
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  DIAG_IGNORE_NEEDS_COMMENT (7.0, "-Wformat-truncation");
+#endif
   snprintf (buf, 100, "%S = %f", tmp, wcstof (tmp, NULL));
+  DIAG_POP_NEEDS_COMMENT;
   printf ("\"%s\" -> %s\n", buf,
 	  strcmp (buf, "81 = 81.000000") == 0 ? "okay" : "buggy");
   result |= strcmp (buf, "81 = 81.000000") != 0;