build: define YY_NO_UNISTD_H only for MSVC#280
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MinGW provides a real unistd.h, and suppressing it leaves the flex generated lexer without a declaration of isatty(), which GCC 14 and later reject as an implicit function declaration. Keep the suppression for MSVC, which has no unistd.h. Signed-off-by: Jiawei Huang <jiawei@tigera.io>
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YY_NO_UNISTD_His currently defined for all Windows targets to keep the flex-generated lexer from including<unistd.h>. That's correct for MSVC, which has nounistd.h, but wrong for MinGW-w64: MinGW ships a realunistd.h, and suppressing it leaves the generated lexer without a declaration ofisatty(), which GCC 14 and later reject as an implicit function declaration (an error by default).Gate the definition on
MSVCso MinGW builds get the realunistd.h. No change for MSVC.Testing
Verified by cross-compiling Fluent Bit (which bundles cmetrics) for Windows from Linux with the Fedora MinGW-w64 UCRT toolchain: the cmetrics prometheus decode lexer compiles instead of failing on the implicit
isattydeclaration. MSVC builds are unaffected — the definition still applies there.