RTS configure: Move over `eventfd` check

This check is for the RTS part of the event manager and has a
corresponding part in `base`.

All of this should boil down to `AC_DEFINE` not `AC_SUBST`, so it
belongs in the RTS configure and should be safe to move without
modification.

Progress towards #17191

configure.ac

@@ -1040,10 +1040,6 @@ AC_LINK_IFELSE([AC_LANG_CALL([], [printf\$LDBLStub])],
 
 FP_CHECK_PTHREADS
 
-dnl ** check for eventfd which is needed by the I/O manager
-AC_CHECK_HEADERS([sys/eventfd.h])
-AC_CHECK_FUNCS([eventfd])
-
 GHC_ADJUSTORS_METHOD([Target])
 AC_SUBST([UseLibffiForAdjustors])
 

rts/configure.ac

@@ -33,6 +33,10 @@ GHC_CONVERT_PLATFORM_PARTS([host], [Host])
 FPTOOLS_SET_PLATFORM_VARS([host], [Host])
 FPTOOLS_SET_HASKELL_PLATFORM_VARS([Host])
 
+dnl ** check for eventfd which is needed by the I/O manager
+AC_CHECK_HEADERS([sys/eventfd.h])
+AC_CHECK_FUNCS([eventfd])
+
 AC_CHECK_FUNCS([getpid getuid raise])
 
 dnl ** Check for __thread support in the compiler