tools: selftests: riscv: Add missing include for vector test

GCC raises the following warning:
warning: 'status' may be used uninitialized
The warning comes from the fact, that the signature of waitpid() is
unknown and therefore the initialization of GCC cannot be guessed.
Let's add the relevant header to address this warning.

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andy Chiu <andy.chiu@sifive.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20231123185821.2272504-4-christoph.muellner@vrull.eu
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

selftests: riscv: Fix compilation error with vstate_exec_nolibc.c

The following error happens:

In file included from vstate_exec_nolibc.c:2:
/usr/include/riscv64-linux-gnu/sys/prctl.h:42:12: error: conflicting types for ‘prctl’; h
ave ‘int(int, ...)’
42 | extern int prctl (int __option, ...) __THROW;
| ^~~~~
In file included from ./../../../../include/nolibc/nolibc.h:99,
from <command-line>:
./../../../../include/nolibc/sys.h:892:5: note: previous definition of ‘prctl’ with type
‘int(int, long unsigned int, long unsigned int, long unsigned int, long unsigned int)
’
892 | int prctl(int option, unsigned long arg2, unsigned long arg3,
| ^~~~~

Fix this by not including <sys/prctl.h>, which is not needed here since
prctl syscall is directly called using its number.

Fixes: 7cf6198ce22d ("selftests: Test RISC-V Vector prctl interface")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20230713115829.110421-1-alexghiti@rivosinc.com
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

selftests: Test RISC-V Vector prctl interface

This add a test for prctl interface that controls the use of userspace
Vector.

Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Link: https://lore.kernel.org/r/20230605110724.21391-27-andy.chiu@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>