C doesn't have function overloading. You're probably looking at C++ code. Unfortunately, even if you compile that code using something like Inline::CPP you're going to have to use different function names in some way, because XS, which is built on C, won't be able to bind two functions in the same namespace with the same name.

use strict;
use warnings;

use Inline CPP => 'DATA';


print add( 1, 1 ), "\n";

print add( 1, 1, 1 ), "\n";

__DATA__
__CPP__

int add ( int a, int b ) {
    return a + b;
}

int add( int a, int b, int c ) {
    return a + b + c;
}
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...outputs...

Usage: main::add(a, b, c) at ./mytest.pl line 7.
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...where line 7 is the add( 1, 1 ) call.

Perl can't be expected to understand C++'s rules for resolving overloading. And since Perl is a dynamic language, the C or C++ linker can't make the decision either.