Bug 23587

We have a system-wide standard for the environment variable OSTYPE that has
been in place for years. Whenever bash is run, it clobbers this variable.
On my platform, it always sets it to linux-gnu. The older versions of Bash
set this to "linux" so this problem has not popped up until now. This
messes up Makefiles because make runs subshells all the time, and the
OSTYPE is being clobbered all the time.

First, I can understand wanting to set this variable, but bash should not
set the variable if it is already set. This is a design decision with which
some may disagree, but you cannot disagree with the second problem here:

Second, when bash is run as sh (e.g., /bin/sh) it is supposed to behave as
much as possible like the old Bourne Shell, yet bash2 still clobbers OSTYPE.

It does the same thing, BTW, with MACHTYPE, etc.

Here's how to reproduce the problem:

% help | grep version
GNU bash, version 2.04.11(1)-release (i386-redhat-linux-gnu)
% export OSTYPE=vxworks-target
% echo $OSTYPE
vxworks-target
% /bin/sh -c 'echo $OSTYPE'
linux-gnu
% (/bin/sh -c 'echo $OSTYPE')
linux-gnu

Here is the same thing run on Solaris:
$ OSTYPE=vxworks-target
$ export OSTYPE
$ echo $OSTYPE
vxworks-target
$ /bin/sh -c 'echo $OSTYPE'
vxworks-target
$ (/bin/sh -c 'echo $OSTYPE')
vxworks-target