cmake fails on macos

[John-Colvin]

Current ldc master. Apple silicon. MacOS 14.1.1

I have seen this with other older ldc releases, other ldc bootstrap compiler versions, also with pointing a standalone llvm, other llvm versions...

It works if I re-run the cmake command, which means something is broken & not idempotent.

john@Johns-MacBook-Pro build % cmake ../ -DD_COMPILER=$HOME/dlang/ldc-1.35.0/bin/ldmd2 -DLLVM_CONFIG=/opt/homebrew/Cellar/llvm@16/16.0.6/bin/llvm-config -DCMAKE_BUILD_TYPE=Release
CMake Deprecation Warning at CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.


-- The C compiler identification is AppleClang 15.0.0.15000040
-- The CXX compiler identification is AppleClang 15.0.0.15000040
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Library/Developer/CommandLineTools/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Library/Developer/CommandLineTools/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found host D compiler /Users/john/dlang/ldc-1.35.0/bin/ldmd2, with default flags ''
-- Host D compiler ID: LDMD
-- Host D compiler version: LDC - the LLVM D compiler (1.35.0)
-- Host D compiler front-end version: 2105
-- LLVM_NATIVE_ARCH: AArch64
-- Found LLVM: /opt/homebrew/Cellar/llvm@16/16.0.6 (found suitable version "16.0.6", minimum required is "11.0") 
-- Using LLVM Version 16.0
-- LDC version identifier: 1.36.0-git-fe74d37-dirty
-- -- Building LDC with dynamic compilation support (LDC_DYNAMIC_COMPILE): OFF
-- -- Building LDC with integrated LLD linker (LDC_WITH_LLD): ON
-- -- Building LDC with enabled assertions (LDC_ENABLE_ASSERTIONS): OFF
CMake Error at cmake/Modules/ExtractDMDSystemLinker.cmake:42 (message):
  Failed to link empty D program using
  '/Users/john/dlang/ldc-1.35.0/bin/ldmd2 -wi':

  ld: library not found for -lpthread

  clang: error: linker command failed with exit code 1 (use -v to see
  invocation)

  Error: /Library/Developer/CommandLineTools/usr/bin/cc failed with status: 1
Call Stack (most recent call first):
  CMakeLists.txt:643 (include)


-- Configuring incomplete, errors occurred!

[kinke]

Duplicate of #3901.