pthread: Rename thread_init to avoid symbol collision

The AIX threads library exposes a function with the same name.

Signed-off-by: Martin Storsjö <martin@martin.st>
fmtconvert: Explicitly use int32_t instead of int

Signed-off-by: Martin Storsjö <martin@martin.st>
Consistently use "cpu_flags" as variable/parameter name for CPU flags