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, 10 insertions, 0 deletions

diff --git a/stdio-common/tstdiomisc.c b/stdio-common/tstdiomisc.c
index 5548a71..9c7342d 100644
--- a/stdio-common/tstdiomisc.c
+++ b/stdio-common/tstdiomisc.c
@@ -94,6 +94,14 @@ F (void)
 
   qnanval = NAN;
 
+  /* The %f and %F arguments are in fact constants, but GCC is
+     prevented from seeing this (volatile is used) so it cannot tell
+     that the output is not truncated.  */
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  DIAG_IGNORE_NEEDS_COMMENT (7.0, "-Wformat-truncation");
+#endif
+
   snprintf (buf, sizeof buf, "%a %A %e %E %f %F %g %G",
 	    qnanval, qnanval, qnanval, qnanval,
 	    qnanval, qnanval, qnanval, qnanval);
@@ -260,6 +268,8 @@ F (void)
   printf ("expected L\"-inf -INF -inf -INF -inf -INF -inf -INF\", got L\"%S\"\n",
 	  wbuf);
 
+  DIAG_POP_NEEDS_COMMENT;
+
   return result;
 }