[PATCH] doc/gdb.texinfo: Add EIO and ENOSYS errno values

[Yodel Eldar <yodel.eldar@yodel.dev>]

This patch adds the EIO and ENOSYS errno values supported by GDB's
File-I/O to section E.14.9: Errno Values of the GDB manual [1] that were
presumably inadvertently omitted; both can be seen in the enum
fileio_error:gdbsupport/fileio.h and corresponding function
host_to_fileio_error:gdbsupport/fileio.cc as FILEIO_{EIO,ENOSYS}.

FILEIO_SUCCESS remains excluded from the manual, because its stated
purpose (commit b872057a6) is to internally represent the absence of an
error value from the remote, and it's not actually an error number.

[1] https://sourceware.org/gdb/current/onlinedocs/gdb.html/Errno-Values.html
---

Notes:
    Simon, please let me know if my exclusion of FILEIO_SUCCESS is a mistake;
    I assumed the doc page was geared towards stub authors, and that they
    typically would check the retcode of a file-op function call before
    converting the nonzero errno to GDB's internal protocol representation
    of the error value as listed in the manual, but perhaps that's too
    myopic; if so, I can resubmit with a "SUCCESS = 0" line added. As the
    originator of the enum and member, I defer to your judgment.
    
    As a side note, I sent this email with my preferred email address that
    is different from my previously used email address,
    yodel.eldar(at)gmail.com. As attestation, I signed this email
    with patatt and the same GPG key as before.
    
    Thanks,
    Yodel

 gdb/doc/gdb.texinfo | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index a13d5c0388e..5b06d3dbcf8 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -48348,6 +48348,7 @@ All values are given in decimal representation.
   EPERM           1
   ENOENT          2
   EINTR           4
+  EIO             5
   EBADF           9
   EACCES         13
   EFAULT         14
@@ -48363,6 +48364,7 @@ All values are given in decimal representation.
   ENOSPC         28
   ESPIPE         29
   EROFS          30
+  ENOSYS         88
   ENAMETOOLONG   91
   EUNKNOWN       9999
 @end smallexample
-- 
2.51.0