Fix unused variable for Win32 build in random_seed.c

[Philosoph228]

CMake Release configuration add the -Werror flag, which fails the compilation if there any warning. There is an only one - unused variable.
Please let compilations succeed with Release configuration.

Build logs:

user@buildhost MINGW64 ~/json-c
$ mkdir build && cd $_

user@buildhost MINGW64 ~/json-c/build
$ cmake .. -G"MSYS Makefiles" -DCMAKE_BUILD_TYPE=Release
-- The C compiler identification is GNU 10.2.0
-- Check for working C compiler: C:/msys64/mingw64/bin/gcc.exe
-- Check for working C compiler: C:/msys64/mingw64/bin/gcc.exe - works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Looking for sys/resource.h
-- Looking for sys/resource.h - not found
-- Wrote C:/msys64/home/user/json-c/build/apps_config.h
-- Looking for fcntl.h
-- Looking for fcntl.h - found
-- Looking for inttypes.h
-- Looking for inttypes.h - found
-- Looking for stdarg.h
-- Looking for stdarg.h - found
-- Looking for strings.h
-- Looking for strings.h - found
-- Looking for string.h
-- Looking for string.h - found
-- Looking for syslog.h
-- Looking for syslog.h - not found
-- Looking for 4 include files stdlib.h, ..., float.h
-- Looking for 4 include files stdlib.h, ..., float.h - found
-- Looking for unistd.h
-- Looking for unistd.h - found
-- Looking for sys/types.h
-- Looking for sys/types.h - found
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-- Looking for dlfcn.h - not found
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-- Looking for endian.h - not found
-- Looking for limits.h
-- Looking for limits.h - found
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-- Looking for locale.h - found
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-- Looking for memory.h - found
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-- Looking for sys/cdefs.h
-- Looking for sys/cdefs.h - found
-- Looking for sys/param.h
-- Looking for sys/param.h - found
-- Looking for sys/random.h
-- Looking for sys/random.h - not found
-- Looking for sys/stat.h
-- Looking for sys/stat.h - found
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-- Looking for xlocale.h - not found
-- Looking for _isnan
-- Looking for _isnan - found
-- Looking for _finite
-- Looking for _finite - found
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-- Looking for arc4random
-- Looking for arc4random - not found
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-- Check size of int
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-- Performing Test HAS_GNU_WARNING_LONG
-- Performing Test HAS_GNU_WARNING_LONG - Failed
-- Performing Test HAVE_ATOMIC_BUILTINS
-- Performing Test HAVE_ATOMIC_BUILTINS - Success
-- Performing Test HAVE___THREAD
-- Performing Test HAVE___THREAD - Success
-- Wrote C:/msys64/home/user/json-c/build/config.h
-- Wrote C:/msys64/home/user/json-c/build/json_config.h
-- Performing Test REENTRANT_WORKS
-- Performing Test REENTRANT_WORKS - Success
-- Performing Test BSYMBOLIC_WORKS
-- Performing Test BSYMBOLIC_WORKS - Success
-- Performing Test VERSION_SCRIPT_WORKS
-- Performing Test VERSION_SCRIPT_WORKS - Success
-- Could NOT find Doxygen (missing: DOXYGEN_EXECUTABLE)
Warning: doxygen not found, the 'doc' target will not be included
-- Configuring done
-- Generating done
-- Build files have been written to: C:/msys64/home/user/json-c/build

user@buildhost MINGW64 ~/json-c/build
$ cd ..

user@buildhost MINGW64 ~/json-c
$ cmake --build ./build --config Release
Scanning dependencies of target json-c
[  1%] Building C object CMakeFiles/json-c.dir/arraylist.c.obj
[  2%] Building C object CMakeFiles/json-c.dir/debug.c.obj
[  3%] Building C object CMakeFiles/json-c.dir/json_c_version.c.obj
[  4%] Building C object CMakeFiles/json-c.dir/json_object.c.obj
[  5%] Building C object CMakeFiles/json-c.dir/json_object_iterator.c.obj
[  7%] Building C object CMakeFiles/json-c.dir/json_pointer.c.obj
[  8%] Building C object CMakeFiles/json-c.dir/json_tokener.c.obj
[  9%] Building C object CMakeFiles/json-c.dir/json_util.c.obj
[ 10%] Building C object CMakeFiles/json-c.dir/json_visit.c.obj
[ 11%] Building C object CMakeFiles/json-c.dir/linkhash.c.obj
[ 13%] Building C object CMakeFiles/json-c.dir/printbuf.c.obj
[ 14%] Building C object CMakeFiles/json-c.dir/random_seed.c.obj
C:/msys64/home/user/json-c/random_seed.c: In function 'get_cryptgenrandom_seed':
C:/msys64/home/user/json-c/random_seed.c:274:6: error: unused variable 'r' [-Werror=unused-variable]
  274 |  int r;
      |      ^
cc1.exe: all warnings being treated as errors
make[2]: *** [CMakeFiles/json-c.dir/build.make:226: CMakeFiles/json-c.dir/random_seed.c.obj] Error 1
make[1]: *** [CMakeFiles/Makefile2:238: CMakeFiles/json-c.dir/all] Error 2
make: *** [Makefile:183: all] Error 2

Build Environment:

user@buildhost MINGW64 ~
$ uname -a
MINGW64_NT-10.0-19041 user@buildhost 3.1.7-340.x86_64 2020-11-08 12:32 UTC x86_64 Msys

user@buildhost MINGW64 ~
$ cmake --version
cmake version 3.17.3

CMake suite maintained and supported by Kitware (kitware.com/cmake).

user@buildhost MINGW64 ~
$ gcc --version
gcc.exe (Rev3, Built by MSYS2 project) 10.2.0
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[coveralls]

Coverage remained the same at 87.382% when pulling 9c05651 on Philosoph228:werror-fix into 041cef4 on json-c:master.

[ploxiln]

The change looks good to me. The PR and commit title could be more concise, maybe something like:

random_seed: fix unused variable for win32 build

It looks like this variable became unused (only for windows builds) in #674 and this project (understandably) only has CI windows tests using msvc (no gcc or clang on windows in CI).

[Philosoph228]

I had opened the commit history and saw it's a really good idea. I'll amend the commit message, thank you.

[Philosoph228]

Um… I am not sure I did it right. Maybe squash changes? Or would I have to try from scratch?

[ploxiln]

No, you don't have to try from scratch. If you amend or rebase, you need to force push. If you just try to push after one of those operations, git will say "not a fast-forward merge, please merge in the remote branch first", so that's what you did, but it's not what you really wanted to do. You wanted to replace the remote state with the new version, rather than merging the new and old versions of your branch.

[ploxiln]

Looks like you figured it out :)