[CMake] Enable LLVM_ENABLE_PER_TARGET_RUNTIME_DIR by default on *BSD

Similar to D107799 but for *BSD (DragonFlyBSD, FreeBSD, NetBSD, OpenBSD, etc).
This Linux default has been in main and release/15.x for a while.

`CMAKE_SYSTEM_PROCESSOR MATCHES "^arm"` is excluded for now.

Link: https://discourse.llvm.org/t/rfc-time-to-drop-legacy-runtime-paths/64628

Reviewed By: dim

Differential Revision: https://reviews.llvm.org/D110126

Author: MaskRay

llvm/CMakeLists.txt

@@ -799,7 +799,7 @@ set(LLVM_TARGET_TRIPLE_ENV CACHE STRING "The name of environment variable to ove
 mark_as_advanced(LLVM_TARGET_TRIPLE_ENV)
 
 # Per target dir not yet supported on Arm 32 bit due to arm vs armhf handling
-if(CMAKE_SYSTEM_NAME MATCHES "Linux" AND NOT CMAKE_SYSTEM_PROCESSOR MATCHES "^arm")
+if(CMAKE_SYSTEM_NAME MATCHES "BSD|Linux" AND NOT CMAKE_SYSTEM_PROCESSOR MATCHES "^arm")
   set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default ON)
 else()
   set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default OFF)