build: fix 'implicit-function-declaration' on OpenHarmony platform

[hqzing]

When I cross-compile Node.js for the OpenHarmony platform, I must add the parameter -Wno-error=implicit-function-declaration.

This is my compile script: https://github.com/hqzing/build-ohos-node/blob/main/build.sh

If I don't add this parameter, I will encounter this error:

../deps/uvwasi/src/uvwasi.c:1444:5: error: call to undeclared function 'seekdir'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
 1444 |     seekdir(dir->dir, cookie);
      |     ^
../deps/uvwasi/src/uvwasi.c:1459:14: error: call to undeclared function 'telldir'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
 1459 |       tell = telldir(dir->dir);
      |              ^
2 errors generated.
make[1]: *** [deps/uvwasi/uvwasi.target.mk:100: /root/build-ohos-node/node-v24.2.0/out/Release/obj.target/uvwasi/deps/uvwasi/src/uvwasi.o] Error 1
make[1]: *** Waiting for unfinished jobs....

Now that I have identified the root cause, which is the missing macro definition _GNU_SOURCE during the build process, I am proposing this PR to fix the issue and eliminate the dependency on -Wno-error=implicit-function-declaration parameter.

[nodejs-github-bot]

Review requested:

• @nodejs/gyp
• @nodejs/security-wg
• @nodejs/wasi

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/68780/

[hqzing]

Too many flaky test, should we retry the CI task? @lpinca @targos @UlisesGascon

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/68812/