Build fails on macOS (Nix)
Building on macOS using Nix fails:
> [16/35] Compiling C object blksum.p/progress.c.o
> FAILED: blksum.p/progress.c.o
> clang -Iblksum.p -I. -I.. -I/nix/store/ppql8r3rp754cll5ys12rkj09j3f0c6i-openssl-3.0.7-dev/include -fcolor-diagnostics -Wall -Winvalid-pch -Wextra -std=gnu99 -fPIE -MD -MQ blksum.p/progress.c.o -MF blksum.p/progress.c.o.d -o blksum.p/progress.c.o -c ../progress.c
> In file included from ../progress.c:8:
> ../blksum.h:66:5: error: unknown type name 'pid_t'
> pid_t pid;
> ^Also fails when building manually on macOS Ventura.
Probably a header is missing after recent change.
We don't have CI on macOS yet, so these issues are likey.