Fix Gawk bug that puts stderr into O_APPEND mode

[Paul Eggert]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -g -O2 -DNDEBUG
uname output: Linux wing 6.11.0-14-generic #15-Ubuntu SMP 
PREEMPT_DYNAMIC Fri Jan 10 23:48:25 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Gawk Version: 5.3.60

Attestation 1:
        I have read 
https://www.gnu.org/software/gawk/manual/html_node/Bugs.html.
        Yes

Attestation 2:
        I have not modified the sources before building gawk.
        True

Description:
        'gawk' puts stderr into O_APPEND mode to work around BSD
        glitches.  Unfortunately this can cause other programs to
        misbehave.  Also, this behavior doesn't conform to POSIX.

        I ran into this issue when someone reported that Gawk put
        /dev/tty into O_APPEND mode, which messed up GNU 'cat'.
        Although this is a bug in GNU 'cat', it's also a bug in Gawk.

Repeat-By:
        Run the following shell commands:
          echo abcdefgh >foo
          (gawk 'BEGIN{}'; echo ouch >&2) 2<>foo
          cat foo

        The output is:
          abcdefgh
          ouch

        The output should be:
          ouch
          fgh


Fix:
        Attached.

0001-Fix-bug-that-put-stderr-into-O_APPEND-mode.patch
Description: Text Data