PPC/s390: [builtins] NonNumberToNumber and StringToNumber now use CallRuntime instead of TailCallRuntime

Port b5c69cbf

Original commit message:

    With the tail call, pointers to the JS heap could be pushed on a
    js-to-wasm frame. On the js-to-wasm frame, however, this pointer would
    not be updated by the GC.

R=ahaas@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG=617084
LOG=N

Review-Url: https://codereview.chromium.org/2085183002
Cr-Commit-Position: refs/heads/master@{#37160}