Port PCRE2 JIT to Linux on IBMz (s390x)

Enable PCRE2 JIT on Linux on IBMz (s390x-linux) and optimize to achieve equivalent speedup over non-JIT code as x86_64. Goal is full functionality and passing testsuite with JIT enabled. An unfinished port of PCRE2 JIT to s390x exists in the Linux-on-IBM-z Github account and can be used as a starting point. IBM will contribute the code as necessary. https://github.com/linux-on-ibm-z/pcre2/tree/s390x-experimental