objtool: Hide unnecessary compiler error message

The check for using old libelf prints an error message when libelf.h is
not available but does not abort. This may confuse so hide the compiler
error message.

Signed-off-by: David Engraf <david.engraf@sysgo.com>
Link: https://lore.kernel.org/r/20250203073610.206000-1-david.engraf@sysgo.com


Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>