Clang "unused function EnableClmul" warning on 32-bit systems

[hebasto]

Compiling Bitcoin Core, the recent master branch (bitcoin/bitcoin@57982f4):

$ clang-12 --version
Ubuntu clang version 12.0.0-3ubuntu1~20.04.4
Target: armv7l-unknown-linux-gnueabihf
Thread model: posix
InstalledDir: /usr/bin
$ make
...
  CXX      minisketch/src/libminisketch_a-minisketch.o
minisketch/src/minisketch.cpp:66:20: warning: unused function 'EnableClmul' [-Wunused-function]
static inline bool EnableClmul()
                   ^
1 warning generated.
...

[ajtowns]

I get this when building bitcoin's fuzzer.

EnableClmul is only invoked when HAVE_CLMUL is defined, so moving the #ifdef HAVE_CLMUL / #endif to wrap the function would solve this.