options/posix: Fix function prototype of pthread_exit #886

Job	Run time
Compile sysdeps (dripos)	1m 26s
Build mlibc (x86_64, mlibc)	15m 47s
Compile sysdeps (lemon)	1m 48s
Build mlibc (x86_64, mlibc-static)	3m 10s
Compile sysdeps (aero)	1m 55s
Build mlibc (x86_64, mlibc-shared)	2m 45s
Compile sysdeps (ironclad)	1m 30s
Build mlibc (x86_64, mlibc-ansi-only)	2m 53s
Compile sysdeps (lyre)	1m 52s
Build mlibc (x86_64, mlibc-headers-only)	1m 45s
Compile sysdeps (keyronex)	1m 40s
Build mlibc (riscv64, mlibc)	3m 48s
Build mlibc (riscv64, mlibc-static)	7m 31s
Build mlibc (riscv64, mlibc-shared)	3m 22s
Build mlibc (riscv64, mlibc-ansi-only)	3m 3s
Build mlibc (riscv64, mlibc-headers-only)	1m 24s
Build mlibc (aarch64, mlibc)	5m 1s
Build mlibc (aarch64, mlibc-static)	4m 11s
Build mlibc (aarch64, mlibc-shared)	3m 14s
Build mlibc (aarch64, mlibc-ansi-only)	2m 59s
Build mlibc (aarch64, mlibc-headers-only)	1m 46s
	1h 12m 50s

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