[libc] fixed target issue with exit_handler (llvm#94678)

- addressed
llvm#94317 (comment)
- added conditional in cmake file for exit_handler object library

Co-authored-by: Aaryan Shukla <aaryanshukla@google.com>

Author: aaryanshukla

libc/src/stdlib/CMakeLists.txt

@@ -416,6 +416,9 @@ add_entrypoint_object(
     libc.src.__support.OSUtil.osutil
 )
 
+# TODO: Move all exit functions to linux specific 
+
+if (TARGET libc.src.__support.threads.mutex)
 add_object_library(
   exit_handler
   SRCS
@@ -432,6 +435,7 @@ add_object_library(
     libc.src.__support.fixedvector
     libc.src.__support.threads.mutex
 )
+endif()
 
 add_entrypoint_object(
   atexit