jit: configure: Explicitly reference 'native' component.

Until recently 'native' was implicitly included via 'orcjit', but a change
included in LLVM 11 (not yet released) removed a number of such indirect
component references.
Reported-By: Fabien COELHO <coelho@cri.ensmp.fr>
Reported-By: Andres Freund <andres@anarazel.de>
Reported-By: Thomas Munro <thomas.munro@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20201201064949.mex6kvi2kygby3ni@alap3.anarazel.de
Backpatch: 11-, where jit support was added

config/llvm.m4

@@ -76,6 +76,7 @@ AC_DEFUN([PGAC_LLVM_SUPPORT],
       debuginfodwarf) pgac_components="$pgac_components $pgac_component";;
       orcjit) pgac_components="$pgac_components $pgac_component";;
       passes) pgac_components="$pgac_components $pgac_component";;
+      native) pgac_components="$pgac_components $pgac_component";;
       perfjitevents) pgac_components="$pgac_components $pgac_component";;
     esac
   done;

configure

@@ -5168,6 +5168,7 @@ fi
       debuginfodwarf) pgac_components="$pgac_components $pgac_component";;
       orcjit) pgac_components="$pgac_components $pgac_component";;
       passes) pgac_components="$pgac_components $pgac_component";;
+      native) pgac_components="$pgac_components $pgac_component";;
       perfjitevents) pgac_components="$pgac_components $pgac_component";;
     esac
   done;