[openwrt/openwrt] grub2: set -std=gnu17

[LEDE Commits]

hauke pushed a commit to openwrt/openwrt.git, branch openwrt-23.05:
https://git.openwrt.org/d903a23de46d061c5849e32f6c2837d11d617534

commit d903a23de46d061c5849e32f6c2837d11d617534
Author: Hauke Mehrtens <hauke at hauke-m.de>
AuthorDate: Sun Jun 8 01:55:18 2025 +0200

    grub2: set -std=gnu17
    
    Arch Linux updated to GCC15 which now defaults to GNU23 as the default
    instead of GNU17[1], and this breaks grub compilation.
    
    This is fixed in more recent grub2 versions.
    
    [1] https://gcc.gnu.org/gcc-15/porting_to.html#c23
    
    Link: https://github.com/openwrt/openwrt/pull/19065
    Signed-off-by: Hauke Mehrtens <hauke at hauke-m.de>
---
 package/boot/grub2/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/package/boot/grub2/Makefile b/package/boot/grub2/Makefile
index 865feee9ad..d7923d7f02 100644
--- a/package/boot/grub2/Makefile
+++ b/package/boot/grub2/Makefile
@@ -73,6 +73,8 @@ endef
 
 HOST_BUILD_PREFIX := $(STAGING_DIR_HOST)
 
+HOST_CFLAGS +=-std=gnu17
+
 CONFIGURE_VARS += \
 	grub_build_mkfont_excuse="don't want fonts"