- Add fibers support for RISCV64
- Disable build on RISCV32 musl since getcontext/setcontext APIs do not
exist on musl which are needed for fibers
- Detailed changes are here [1]
[1] https://www.php.net/ChangeLog-8.php#PHP_8_1
Signed-off-by: Khem Raj <raj.khem@gmail.com>