[Plat-10822] Fix for duplicate C++ library warnings

[kstenerud]

Goal

Xcode 15 now warns about duplicate library flags during the linking phase.

Since c++ is now inferred by the compiler, adding -lc++ hasn't been necessary in Xcode for the past few versions.

This PR removes the manual -lc++ flags.

Testing

Reran all tests to ensure that this doesn't break any builds.

[github-actions]

Bugsnag.framework binary size did not change - 713,488 bytes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.3%     +48  +0.3%     +48    [__TEXT]
  -1.4%     -48  -1.4%     -48    [Mach-O Headers]
  [ = ]       0  [ = ]       0    TOTAL

Generated by 🚫 Danger