filterdiff: error: assignment of read-only variable 'stdout' (on musl)

[hhoffstaette]

Looks like a last-minute change for support of --in-place changed something that does not compile on musl..again:

gcc -DHAVE_CONFIG_H -I.   -D_GNU_SOURCE -D_FORTIFY_SOURCE=2 -I./src -I./lib -I./lib -pipe -O2 -Wall -MT src/filterdiff.o -MD -MP -MF $depbase.Tpo -c -o src/filterdiff.o src/filterdiff.c &&\
mv -f $depbase.Tpo $depbase.Po
src/filterdiff.c: In function 'main':
src/filterdiff.c:1833:40: error: assignment of read-only variable 'stdout'
 1833 |                                 stdout = temp_output;
      |                                        ^
src/filterdiff.c:1838:40: error: assignment of read-only variable 'stdout'
 1838 |                                 stdout = old_stdout;
      |                                        ^

Musl does not support stdin/stdout/stderr reassignment.
In case you're wondering about the reasons.

[hhoffstaette]

I hax0red something together here - it passes the test suite just like on glibc. I hate introducing an almost-copy of xtmpfile() but there really is no better way with the current design. If we really wanted, we could make the fd argument optional and act like xtmpfile() if it's null or something, though that would probably make things worse.
Please take a look and let me know what you think.

[twaugh]

I think that looks like a good solution. Want to submit a PR?
Hopefully the new CI tests will make this fix stick. :)

[hhoffstaette]

I removed the change of the gnulib repo, though maybe you want to re-add it for yourself? Savanna is recently often just plain unreachable/times out.