security/rustls-ffi: fix build on powerpc64le
[ 97%] Building C object aws-lc/crypto/fipsmodule/CMakeFiles/fipsmodule.dir/bcm.c.o
In file included from /wrkdirs/usr/ports/security/rustls-ffi/work/rustls-ffi-0.14.1/cargo-crates/aws-lc-sys-0.21.1/aws-lc/crypto/fipsmodule/bcm.c:83:
/wrkdirs/usr/ports/security/rustls-ffi/work/rustls-ffi-0.14.1/cargo-crates/aws-lc-sys-0.21.1/aws-lc/crypto/fipsmodule/cpucap/cpu_ppc64le.c:72:28: error: call to undeclared function 'getauxval'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
72 | OPENSSL_ppc64le_hwcap2 = getauxval(AT_HWCAP2);
| ^
1 error generated.