Add AArch64 support for libpasastro package

[cgobat]

I have tested this updated PKGBUILD using makepkg and then pacman -U on armv8l. The package builds and installs successfully.

No changes are needed in order to add ARM support other than adding it to the arch array.

[Integral-Tech]

AArch64 PKGBUILDs are separately placed in alarmcn directory. If you expect compiled binaries for Arch Linux ARM, you should copy archlinuxcn/libpasastro directory into alarmcn and change the maintainer to yourself.

[oldherl]

AArch64 PKGBUILDs are separately placed in alarmcn directory. If you expect compiled binaries for Arch Linux ARM, you should copy archlinuxcn/libpasastro directory into alarmcn and change the maintainer to yourself.

I suspect that he cares mainly for the AUR (which is maintained by me and updated by lilac), rather than the aarch64 port of [archlinuxcn].

I will try and test this package on aarch64 and consider adding this.