tools: elfutils: set -std=gnu17

tools: elfutils: set -std=gnu17

Fedora 42 updated to GCC15 which now defaults to GNU23 as the default
instead of GNU17[1], and this breaks m4 compilation.

This looks like a gnulib issue, so until that is updated/fixed
lets simply set C language version back to GNU17.

[1] https://gcc.gnu.org/gcc-15/porting_to.html#c23

Link: https://github.com/openwrt/openwrt/pull/18506
Signed-off-by: Robert Marko <[email protected]>