Port over illumos fixes for conf.sh (#361)

This commit ports over two of Andy Fiddaman's bugfixes to conf.sh
on illumos:

- The compiler isn't passed on to an invocation of iffe. The bugfix is
  from this commit: <63563232>
- The getconf builtin is missing several parameters on illumos.
  Reproducer:
     $ /opt/ast/bin/getconf ADDRESS_WIDTH
     getconf: Invalid argument (ADDRESS_WIDTH)  # Should output '64'
  This bug occurs because conf.sh expects GNU sed and fails to work
  properly with other sed implementations. The bugfix and original bug
  report can be found here:
  https://www.illumos.org/issues/14044
  ba443cfd

NEWS

@@ -3,6 +3,11 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2021-12-05:
+
+- Fixed an issue on illumos that caused some parameters in the getconf
+  builtin to fail.
+
 2021-12-01:
 
 - Fixed a memory fault that occurred when a discipline function exited