gdbm: Use C11 standard

GCC15 is switching defaults to C23 and gdbm is not yet ready to
compile using C23 std.

(From OE-Core rev: e0f13f9bc96a0dd4c5f6750a8106422a6d015359)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-support/gdbm/gdbm_1.24.bb

@@ -23,6 +23,9 @@ EXTRA_OECONF = "--enable-libgdbm-compat --without-readline"
 # Stop presence of dbm/nbdm on the host contaminating builds
 CACHED_CONFIGUREVARS += "ac_cv_lib_ndbm_main=no ac_cv_lib_dbm_main=no"
 
+# Not yet ready for C23
+CFLAGS += "-std=gnu11"
+
 BBCLASSEXTEND = "native nativesdk"
 
 do_install:append () {