Include errors with compatibility headers in v6-alpha

[rth7680]

capstone/include/capstone/arm64.h

Line 11 in 7624269

#include <capstone/aarch64.h>

and

capstone/include/capstone/systemz_compatibility.h

Line 12 in 7624269

#include <capstone/systemz.h>

use <capstone/...> to include, whereas everything else uses "".

This fails when using -I$includedir because <> only searches system headers.

Either capstone.pc should use -isystem, or these two instances should also use "".