Fix a SHOPT_DEVFD process substitution file descriptor

This commit fixes a long-standing bug that caused a file
descriptor leak when passing a process substitution to a
function. The leak only occured when ksh was compiled with
SHOPT_DEVFD; the FIFO method was unaffected.

src/cmd/ksh93/sh/xec.c:
- When a process substitution is passed to a builtin, the
  remaining file descriptor is closed with sh_iorestore.
  Do the same thing when passing a process substitution
  to a function.
- This fix alone isn't enough, as a file descriptor leak
  could still occur if 'command' was given a function as an
  argument, then passed a process substitution. Add another
  sh_iorestore in this edge case to fix the second file
  descriptor leak.

src/cmd/ksh93/include/defs.h:
- Since the file descriptor leak is now fixed, remove the
  workaround that forced ksh to use the FIFO method.

Fixes: ksh93#67

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.
 
+2021-03-12:
+
+- Fixed a file descriptor leak that occurred when ksh used /dev/fd for
+  process substitutions passed to functions.
+
 2021-03-11:
 
 - Fixed an intermittent bug that caused process substitutions to infinitely

src/cmd/ksh93/include/defs.h

@@ -43,14 +43,6 @@
 #   define mbmax()	1
 #endif
 
-/*
- * Until a file descriptor leak with process substitution
- * is fixed, disable /dev/fd use to avoid the problem.
- * https://github.com/ksh93/ksh/issues/67
- */
-#undef SHOPT_DEVFD
-#define SHOPT_DEVFD	0
-
 #include	<sfio.h>
 #include	<error.h>
 #include	"FEATURE/externs"

src/cmd/ksh93/sh/xec.c

@@ -1542,6 +1542,8 @@ int sh_exec(register const Shnode_t *t, int flags)
 						sh_popcontext(shp,buffp);
 						sh_iorestore(shp,indx,jmpval);
 					}
+					if(shp->topfd>topfd)
+						sh_iorestore(shp,topfd,jmpval);
 					if(nq)
 						unset_instance(nq,&node,&nr,mode);
 					sh_funstaks(slp->slchild,-1);
@@ -1550,6 +1552,8 @@ int sh_exec(register const Shnode_t *t, int flags)
 						siglongjmp(*shp->jmplist,jmpval);
 					goto setexit;
 				}
+				else if(command && shp->topfd>topfd)
+					sh_iorestore(shp,topfd,0);
 			}
 			else if(!io)
 			{