check-uapi: link into shared objects

While testing ABI changes across all architectures, I found that abidiff
sometimes produces nonsensical output. Further debugging identified
missing or broken libelf support for architecture specific relocations
in ET_REL binaries as the source of the problem[1].

Change the script to no longer produce a relocatable object file but
instead create a shared library for each header. This makes abidiff
work for all of the architectures in upstream linux kernels.

Link: https://sourceware.org/bugzilla/show_bug.cgi?id=33869
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20260306163309.2015837-2-arnd@kernel.org
Signed-off-by: Nicolas Schier <nsc@kernel.org>

scripts/check-uapi.sh

@@ -178,8 +178,11 @@ do_compile() {
 	local -r inc_dir="$1"
 	local -r header="$2"
 	local -r out="$3"
-	printf "int main(void) { return 0; }\n" | \
-		"$CC" -c \
+	printf "int f(void) { return 0; }\n" | \
+		"$CC" \
+		  -shared \
+		  -nostdlib \
+		  -fPIC \
 		  -o "$out" \
 		  -x c \
 		  -O0 \