[PATCH v2] config.sub: Work around command assignment bug in some shells.

[Nick Bowler]

When combining variable assignments with a shell command, some older
shells (notably heirloom-sh and presumably also Solaris 10 /bin/sh)
have a bug which causes the assignment to alter the current execution
environment whenever the command is a shell built-in.  For example:

  % dash -c 'x=good; x=bad echo >/dev/null; echo $x'
  good

  % jsh -c 'x=good; x=bad echo >/dev/null; echo $x'
  bad

The config.sub script contains a few commands of the form:

  IFS=- read ...

which triggers this bug, causing the IFS assignment to persist for the
remainder of the script.  This can cause misbehaviour in certain cases,
for example:

  % jsh config.sub i386-linux-gnu
  config.sub: test: unknown operator gnu

  % jsh config.sub i386-gnu/linux
  sed: can't read s|gnu/linux|gnu|: No such file or directory
  Invalid configuration `i386-gnu/linux': OS `' not recognized

* config.sub: Save and restore IFS explicitly to avoid shell bugs.
---
 config.sub | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

 v2: Use 'echo' instead of ':' in the bug demonstration.

diff --git a/config.sub b/config.sub
index d80c5d7..5c36ad7 100755
--- a/config.sub
+++ b/config.sub
@@ -121,9 +121,10 @@ esac
 
 # Split fields of configuration type
 # shellcheck disable=SC2162
-IFS="-" read field1 field2 field3 field4 <<EOF
+save_IFS=$IFS; IFS="-" read field1 field2 field3 field4 <<EOF
 $1
 EOF
+IFS=$save_IFS
 
 # Separate into logical components for further validation
 case $1 in
@@ -931,9 +932,10 @@ case $basic_machine in
 
        *-*)
                # shellcheck disable=SC2162
-               IFS="-" read cpu vendor <<EOF
+               save_IFS=$IFS; IFS="-" read cpu vendor <<EOF
 $basic_machine
 EOF
+               IFS=$save_IFS
                ;;
        # We use `pc' rather than `unknown'
        # because (1) that's what they normally are, and
@@ -1313,9 +1315,10 @@ case $basic_os in
                ;;
        *-*)
                # shellcheck disable=SC2162
-               IFS="-" read kernel os <<EOF
+               save_IFS=$IFS; IFS="-" read kernel os <<EOF
 $basic_os
 EOF
+               IFS=$save_IFS
                ;;
        # Default OS when just kernel was specified
        nto*)
-- 
2.31.1