- TARGET_OS_OSX is not always defined on macOS
- this leads to missing symbol Curl_macos_init()
- TargetConditionals.h seems to define these only when
dynamic targets are enabled (somewhere?)
- this PR fixes that on my macOS 13.4.1
- I have no clue why CI builds worked without it
Follow-up to c7308592fbCloses#11417
https://github.com/curl/curl/pull/7121 introduced a macOS system call
to `SCDynamicStoreCopyProxies`, which is invoked every time an IP
address needs to be resolved.
However, this system call is not thread-safe, and macOS will kill the
process if the system call is run first in a fork. To make it possible
for the parent process to call this once and prevent the crash, only
invoke this system call in the global initialization routine.
In addition, this change is beneficial because it:
1. Avoids extra macOS system calls for every IP lookup.
2. Consolidates macOS-specific initialization in a separate file.
Fixes#11252Closes#11254
