THRIFT-5738: Unused variable fails mac builds

[jeffalder]

Building 0.19.0 on Mac OS Ventura 13.6 (Darwin J59JPHTWW7 22.6.0 Darwin Kernel Version 22.6.0: Fri Sep 15 13:41:28 PDT 2023; root:xnu-8796.141.3.700.8~1/RELEASE_ARM64_T6000 arm64) yields this error:

src/thrift/generate/t_java_generator.cc:5759:9: error: variable 'j' set but not used [-Werror,-Wunused-but-set-variable]
    int j = 0;
        ^
1 error generated.
make[1]: *** [src/thrift/generate/thrift-t_java_generator.o] Error 1

It's a pretty easy excision.

% gcc --version
Apple clang version 15.0.0 (clang-1500.0.40.1)
Target: arm64-apple-darwin22.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

With this change only, the compiler make succeeds.

% cd compiler/cpp
% make -j3 >&/dev/null
% ./thrift --version
Thrift version 0.19.0
% file thrift
thrift: Mach-O 64-bit executable arm64

• Did you create an Apache Jira ticket? (Request account here, not required for trivial changes) https://issues.apache.org/jira/browse/THRIFT-5738
• If a ticket exists: Does your pull request title follow the pattern "THRIFT-NNNN: describe my issue"?
• Did you squash your changes to a single commit? (not required, but preferred)
• Did you do your best to avoid breaking changes? If one was needed, did you label the Jira ticket with "Breaking-Change"?
• n/a If your change does not involve any code, include [skip ci] anywhere in the commit message to free up build resources.

[jeffalder]

Thanks @Jens-G !