Reproducible Builds

[flatcap]

NeoMutt can now be built reproducibly.
Thanks for the pointers, @charles2910

tl;dr

# Map actual build location to a fixed "/home/build"
export CFLAGS="-ffile-prefix-map=$(pwd)=/home/build"

# Configure NeoMutt with a new option
./configure --disable-paths-in-cflags

# Build as normal
make

---

The old configure option --disable-include-path-in-cflags has been deprecated.
I'll document the process more fully when I get the time.

/cc @neomutt/downstream-packagers