Sync -Wno-implicit-fallthrough

This is a sync of the php#6252:
- ext/date: seems to be also fixed

Synced in 743d1fd:
- ext/hash
- ext/opcache
- ext/pcre

Author: petk

ext/date/config0.m4

@@ -4,11 +4,7 @@ AC_CHECK_HEADERS([io.h])
 dnl Check for strtoll, atoll
 AC_CHECK_FUNCS([strtoll atoll])
 
-AX_CHECK_COMPILE_FLAG([-Wno-implicit-fallthrough],
-  [PHP_DATE_CFLAGS="$PHP_DATE_CFLAGS -Wno-implicit-fallthrough"],,
-  [-Werror])
-
-PHP_DATE_CFLAGS="$PHP_DATE_CFLAGS -I@ext_builddir@/lib -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 -DHAVE_TIMELIB_CONFIG_H=1"
+PHP_DATE_CFLAGS="-I@ext_builddir@/lib -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 -DHAVE_TIMELIB_CONFIG_H=1"
 timelib_sources="lib/astro.c lib/dow.c lib/parse_date.c lib/parse_tz.c lib/parse_posix.c
                  lib/timelib.c lib/tm2unixtime.c lib/unixtime2tm.c lib/parse_iso_intervals.c lib/interval.c"