Fixes a 64-bit bug that led to a non-zero pointer on some systems and a subsequent test failure. Using NULL works for both 32-bit and 64-bit.
Additionally:
- Adds missing implicit registers to clobber list of syscall inline asm.
- Adds yet another version for pselect6, in inline asm. The test is semantically redundant to the existing NULL pointer test, and would only expose unexpected changes in glibc's syscall() implementation. Added for completeness.
- Casts every parameter passed to variadic function syscall() into their safe type according to their function definiton.
- Fixes all types passed in asm volatile statements as well.
- Makes all parameters named in asm volatile statements.
Fixes #3911 (closed)