CCFLAGS => '-Wall -g -O2 --std=gnu99',

[download]
I recall MakeMaker replaces CCFLAGS, instead of adding to them. For example, on my system 
$ $ perl -MConfig -E 'say $Config{ccflags}'
-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/loc
+al/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOUR
+CE=2

[download]
I think compiling XS with wrong CCFLAGS (that don't match the perl's ones) is likely to cause some problems with perl interp size, which is what is mismatched in your .so file (and also other problems). Try: 
use Config;

...
   CCFLAGS => "--std=gnu99 $Config{ccflags}", # if that works, add oth
+er stuff, like -g and -Wall...
...

[download]
That's just an idea, so let us know if that works.

In reply to Re: "loadable library" mismatch on new installation by Anonymous Monk
in thread "loadable library" mismatch on new installation by halfcountplus

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