coreutils: Fix gcc14 compilation via std=c17

Fix compilation with gcc 14 by applying the -std=c17 flag, as suggested
by lededev in 2d3f68cc8c (commitcomment-153860241)
(also -c23 seems to work ok with gcc14, but that seems to break gcc13)

Remove the previous autoreconf fix attempt.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>

utils/coreutils/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=coreutils
 PKG_VERSION:=9.6
-PKG_RELEASE:=4
+PKG_RELEASE:=5
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=@GNU/coreutils
@@ -22,9 +22,6 @@ PKG_CPE_ID:=cpe:/a:gnu:coreutils
 
 PKG_INSTALL:=1
 PKG_BUILD_PARALLEL:=1
-ifeq ($(CONFIG_GCC_VERSION_14),y)
-	PKG_FIXUP:=autoreconf
-endif
 
 include $(INCLUDE_DIR)/package.mk
 
@@ -134,6 +131,8 @@ CONFIGURE_ARGS += \
 	--without-selinux \
 	--with-gmp
 
+TARGET_CFLAGS += -std=c17
+
 define Package/coreutils/install
 	true
 endef