[compiler-rt][RISCV] Avoid using __init_riscv_feature_bits as a direc… (#115316)
…t constructor
`__init_riscv_feature_bits` takes an argument that can be
platform-specific, potentially pointing to the VDSO address of the
hwprobe system call for Linux. However, marking it as a constructor does
not guarantee that 0/NULL will always be passed to this argument, which
may result in treating an uninitialized or garbage value as a pointer to
hwprobe, leading to a crash.
The simplest solution is to introduce a small constructor function to
ensure that the platform-specific argument is set to 0/NULL.