Force C locale in LC_NUMERIC when calling cmsGetPostScriptCSA

Use uselocale if available so we only change the current thread, if not
available (i.e. non posix, we hope the process is not doing anything
numeric related in a different thread)

Otherwise we get brokenly formatted PS
7 jobs for fix_lcms_broken_ps in 3 minutes and 41 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #3471766
build

00:03:03

passed #3471771
build_android

00:02:29

passed #3471767
build_clang_libcpp

00:03:40

passed #3471770
build_clazy

00:01:58

passed #3471769
build_mingw64_fedora

00:02:33

passed #3471768
build_ubuntu_16_04

00:02:09

passed #3471765
clang_format

00:00:54