use strcmp to do basic test instead of fmax

Since fmax may be in the math library.  Specifically this test didn't
work on Straberry Perl because fmax could not be found.  strcmp should
be safer.

Author: plicease

t/basic.t

@@ -1,8 +1,9 @@
 use strict;
 use warnings;
-use Test::More tests => 1;
+use Test::More tests => 2;
 
 use parent qw(NativeCall);
 
-sub fmax :Args(double, double) :Native :Returns(double) {}
-is fmax(2.0, 3.0), 3.0;
+sub strcmp :Args(string,string) :Native :Returns(int) {}
+is strcmp("abc","abc"), 0;
+isnt strcmp("abc","def"), 0;