diff --git a/llvm/cmake/config-ix.cmake b/llvm/cmake/config-ix.cmake
index 8726b3d617a8c..38f339d17c852 100644
--- a/llvm/cmake/config-ix.cmake
+++ b/llvm/cmake/config-ix.cmake
@@ -17,6 +17,86 @@ include(CheckCompilerVersion)
 include(CheckProblematicConfigurations)
 include(HandleLLVMStdlib)
 
+if (ANDROID OR CYGWIN OR CMAKE_SYSTEM_NAME MATCHES "AIX|DragonFly|FreeBSD|Haiku|Linux|NetBSD|OpenBSD|SunOS")
+  set(HAVE_DLFCN_H 1)
+  set(HAVE_MACH_MACH_H 0)
+  set(HAVE_MALLOC_MALLOC_H 0)
+  set(HAVE_PTHREAD_H 1)
+  set(HAVE_SIGNAL_H 1)
+  set(HAVE_SYS_IOCTL_H 1)
+  set(HAVE_SYS_MMAN_H 1)
+  set(HAVE_SYS_PARAM_H 1)
+  set(HAVE_SYS_RESOURCE_H 1)
+  set(HAVE_SYS_STAT_H 1)
+  set(HAVE_SYS_TIME_H 1)
+  set(HAVE_SYSEXITS_H 1)
+  set(HAVE_TERMIOS_H 1)
+  set(HAVE_UNISTD_H 1)
+elseif (APPLE)
+  set(HAVE_DLFCN_H 1)
+  set(HAVE_MACH_MACH_H 1)
+  set(HAVE_MALLOC_MALLOC_H 1)
+  set(HAVE_PTHREAD_H 1)
+  set(HAVE_SIGNAL_H 1)
+  set(HAVE_SYS_IOCTL_H 1)
+  set(HAVE_SYS_MMAN_H 1)
+  set(HAVE_SYS_PARAM_H 1)
+  set(HAVE_SYS_RESOURCE_H 1)
+  set(HAVE_SYS_STAT_H 1)
+  set(HAVE_SYS_TIME_H 1)
+  set(HAVE_SYSEXITS_H 1)
+  set(HAVE_TERMIOS_H 1)
+  set(HAVE_UNISTD_H 1)
+elseif (PURE_WINDOWS)
+  set(HAVE_DLFCN_H 0)
+  set(HAVE_MACH_MACH_H 0)
+  set(HAVE_MALLOC_MALLOC_H 0)
+  set(HAVE_PTHREAD_H 0)
+  set(HAVE_SIGNAL_H 1)
+  set(HAVE_SYS_IOCTL_H 0)
+  set(HAVE_SYS_MMAN_H 0)
+  set(HAVE_SYS_PARAM_H 0)
+  set(HAVE_SYS_RESOURCE_H 0)
+  set(HAVE_SYS_STAT_H 1)
+  set(HAVE_SYS_TIME_H 0)
+  set(HAVE_SYSEXITS_H 0)
+  set(HAVE_TERMIOS_H 0)
+  set(HAVE_UNISTD_H 0)
+elseif (ZOS)
+  # Confirmed in
+  # https://github.com/llvm/llvm-project/pull/104706#issuecomment-2297109613
+  set(HAVE_DLFCN_H 1)
+  set(HAVE_MACH_MACH_H 0)
+  set(HAVE_MALLOC_MALLOC_H 0)
+  set(HAVE_PTHREAD_H 1)
+  set(HAVE_SIGNAL_H 1)
+  set(HAVE_SYS_IOCTL_H 1)
+  set(HAVE_SYS_MMAN_H 1)
+  set(HAVE_SYS_PARAM_H 0)
+  set(HAVE_SYS_RESOURCE_H 1)
+  set(HAVE_SYS_STAT_H 1)
+  set(HAVE_SYS_TIME_H 1)
+  set(HAVE_SYSEXITS_H 0)
+  set(HAVE_TERMIOS_H 1)
+  set(HAVE_UNISTD_H 1)
+else()
+  # Other platforms that we don't promise support for.
+  check_include_file(dlfcn.h HAVE_DLFCN_H)
+  check_include_file(mach/mach.h HAVE_MACH_MACH_H)
+  check_include_file(malloc/malloc.h HAVE_MALLOC_MALLOC_H)
+  check_include_file(pthread.h HAVE_PTHREAD_H)
+  check_include_file(signal.h HAVE_SIGNAL_H)
+  check_include_file(sys/ioctl.h HAVE_SYS_IOCTL_H)
+  check_include_file(sys/mman.h HAVE_SYS_MMAN_H)
+  check_include_file(sys/param.h HAVE_SYS_PARAM_H)
+  check_include_file(sys/resource.h HAVE_SYS_RESOURCE_H)
+  check_include_file(sys/stat.h HAVE_SYS_STAT_H)
+  check_include_file(sys/time.h HAVE_SYS_TIME_H)
+  check_include_file(sysexits.h HAVE_SYSEXITS_H)
+  check_include_file(termios.h HAVE_TERMIOS_H)
+  check_include_file(unistd.h HAVE_UNISTD_H)
+endif()
+
 if( UNIX AND NOT (APPLE OR BEOS OR HAIKU) )
   # Used by check_symbol_exists:
   list(APPEND CMAKE_REQUIRED_LIBRARIES "m")
@@ -58,19 +138,6 @@ if(LLVM_USING_GLIBC)
 endif()
 
 # include checks
-check_include_file(dlfcn.h HAVE_DLFCN_H)
-check_include_file(malloc/malloc.h HAVE_MALLOC_MALLOC_H)
-if( NOT PURE_WINDOWS )
-  check_include_file(pthread.h HAVE_PTHREAD_H)
-endif()
-check_include_file(signal.h HAVE_SIGNAL_H)
-check_include_file(sys/ioctl.h HAVE_SYS_IOCTL_H)
-check_include_file(sys/mman.h HAVE_SYS_MMAN_H)
-check_include_file(sys/resource.h HAVE_SYS_RESOURCE_H)
-check_include_file(sys/time.h HAVE_SYS_TIME_H)
-check_include_file(sysexits.h HAVE_SYSEXITS_H)
-check_include_file(termios.h HAVE_TERMIOS_H)
-check_include_file(unistd.h HAVE_UNISTD_H)
 check_include_file(valgrind/valgrind.h HAVE_VALGRIND_VALGRIND_H)
 check_symbol_exists(FE_ALL_EXCEPT "fenv.h" HAVE_DECL_FE_ALL_EXCEPT)
 check_symbol_exists(FE_INEXACT "fenv.h" HAVE_DECL_FE_INEXACT)
@@ -86,7 +153,6 @@ check_c_source_compiles("
         int main(void) { return 0; }"
         HAVE_BUILTIN_THREAD_POINTER)
 
-check_include_file(mach/mach.h HAVE_MACH_MACH_H)
 check_include_file(CrashReporterClient.h HAVE_CRASHREPORTERCLIENT_H)
 if(APPLE)
   check_c_source_compiles("