devel/pecl-grpc: fix build on powerpc64le

Error:
In file included from /wrkdirs/usr/ports/devel/pecl-grpc/work-php74/grpc-1.32.0/third_party/abseil-cpp/absl/base/internal/unscaledcycleclock.cc:27:
/usr/include/sys/sysctl.h:1184:25: error: unknown type name 'u_int'
int sysctl(const int *, u_int, void *, size_t *, const void *, size_t);