strtok -> strtok_r

Otherwise we have threading issues if two threads are doing strtok at
the same time

Fixes issue #1050
7 jobs for strtok_is_bad in 4 minutes and 40 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #7611033
build

00:02:55

passed #7611038
build_android

00:00:44

passed #7611034
build_clang_libcpp

00:04:40

passed #7611037
build_clazy

00:03:39

passed #7611036
build_mingw64_fedora

00:01:59

passed #7611035
build_ubuntu_16_04

00:02:12

passed #7611032
clang_format

00:00:53