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, 3 insertions, 2 deletions

diff --git a/stdio-common/tst-printf.c b/stdio-common/tst-printf.c
index 74150c5e54..719b3eb08c 100644
--- a/stdio-common/tst-printf.c
+++ b/stdio-common/tst-printf.c
@@ -33,8 +33,9 @@
 DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Wformat");
 
 #if __GNUC_PREREQ (7, 0)
-/* Compiler warnings about format lengths should also be ignored.  */
-DIAG_IGNORE_NEEDS_COMMENT (7.0, "-Wformat-length");
+/* Compiler warnings about snprintf output truncation should also be
+   ignored.  */
+DIAG_IGNORE_NEEDS_COMMENT (7.0, "-Wformat-truncation");
 #endif
 
 static void rfg1 (void);