9610b0d1e2 randomenv: Fix MinGW dllimport warning for `environ` (Lőrinc)
Pull request description:
Related to https://github.com/bitcoin/bitcoin/pull/33550#issuecomment-3378978210
Extends 7703884 to guard environ declaration on all Windows builds, not just MSVC.
In the `mingw-w64` headers (used by `llvm-mingw`), `environ` is defined as a macro which expands through [`_environ`](cdb052f1d4/mingw-w64-headers/crt/stdlib.h (L262-L264)) to `(* __p__environ())`, a call to a `dllimport` function, causing the same inconsistent linkage warning as MSVC.
Use `WIN32` instead of `_MSC_VER` to match the platform-specific guards already used throughout the file.
The warning occurs with `llvm-mingw` (both `UCRT` and `MSVCRT` variants as tested by Hebasto), but not with the `mingw-w64` toolchain currently used in CI (as mentioned by fanquake).
----
The error was reproduced by adding a temporary [nightly build](https://github.com/l0rinc/bitcoin-core-nightly/pull/4) pointing to https://github.com/l0rinc/bitcoin/pull/45. On `master` the failure can be seen in https://github.com/l0rinc/bitcoin-core-nightly/pull/2
before:
https://github.com/l0rinc/bitcoin-core-nightly/actions/runs/18327936488/job/52196728885?pr=2
<details>
<summary>Details</summary>
```
/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/src/randomenv.cpp:61:15: warning: '__p__environ' redeclared without 'dllimport' attribute: previous 'dllimport' ignored [-Winconsistent-dllimport]
61 | extern char** environ; // NOLINT(readability-redundant-declaration): Necessary on some platforms
| ^
/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/llvm_mingw_toolchain/aarch64-w64-mingw32/include/stdlib.h:656:17: note: expanded from macro 'environ'
656 | #define environ _environ
| ^
/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/llvm_mingw_toolchain/aarch64-w64-mingw32/include/stdlib.h:225:21: note: expanded from macro '_environ'
225 | #define _environ (* __p__environ())
| ^
/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/llvm_mingw_toolchain/aarch64-w64-mingw32/include/stdlib.h:221:27: note: previous declaration is here
221 | _CRTIMP char ***__cdecl __p__environ(void);
| ^
/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/llvm_mingw_toolchain/aarch64-w64-mingw32/include/stdlib.h:221:3: note: previous attribute is here
221 | _CRTIMP char ***__cdecl __p__environ(void);
| ^
/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/llvm_mingw_toolchain/aarch64-w64-mingw32/include/_mingw.h:52:40: note: expanded from macro '_CRTIMP'
52 | # define _CRTIMP __attribute__ ((__dllimport__))
| ^
1 warning generated.
```
</details>
after:
https://github.com/l0rinc/bitcoin-core-nightly/actions/runs/18329616268/job/52201940831?pr=4
<details>
<summary>Details</summary>
```
[ 28%] Building CXX object src/util/CMakeFiles/bitcoin_util.dir/__/randomenv.cpp.obj
```
</details>
Note that there are some other remaining warnings in the logs that will be fixed in separate PRs
ACKs for top commit:
sipa:
utACK 9610b0d1e2 if this makes the compilers happy
laanwj:
Code review ACK 9610b0d1e2
hebasto:
re-ACK 9610b0d1e2.
Tree-SHA512: a9e39d288b663ed24cbbbae228850e6f02d417d8781a3ac3d0b3db0b7ff734bbd62fddb9f57b8f77daab4e9c016ff66906ebc5fb2de7635ef539ef7f4dc2eaba
98c4994d0f