perl-cross: Correct function signatures in configure_func.sh

There are latent issues in function detection which were succeeding due
to compiler being lenient, but this is fast changing e.g. clang-15 has
turned the -Wimplicit-function-declaration into error which ends up
failing these tests and rightly so. Therefore try to improve the tests
to have proper prototypes known during compilation

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>