gdbm: upgrade 1.24 -> 1.26

gdbm: upgrade 1.24 -> 1.26

Removed c11 flag, as it seems to build fine now with default flags.

ptests passed:

All 38 tests were successful.
DURATION: 11
END: /usr/lib/gdbm/ptest
2025-08-01T18:37
STOP: ptest-runner
TOTAL: 1 FAIL: 0

Changelog:

1.26:
- Fixed build with musl libc
- Fixed build on MacOS
- Improved testsuite

1.25:
- New function: gdbm_open_ext
This function provides a general-purpose interface for opening and
creating GDBM files.  It combines the possibilities of gdbm_open and
gdbm_fd_open and provides detailed control over database file locking.

- New gdbmtool command: collisions
The command prints the collision chains for the current bucket, or for
buckets identified by its arguments.

- Pipelines in gdbmtool
The output of a gdbmtool command can be connected to the input of a
shell command using the traditional pipeline syntax.

- Fix a bug in block coalescing code

Signed-off-by: Gyorgy Sarvari <skandigraun@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>