Runtime: Re-add support for Arch Linux PKGBUILDs.

Originally done in neovim#1087, but was accidentally removed in neovim#4595.

Resolves neovim#4613, resolves neovim#4667.

runtime/filetype.vim

@@ -1858,7 +1858,7 @@ au BufNewFile,BufRead sgml.catalog*		call s:StarSetf('catalog')
 
 " Shell scripts (sh, ksh, bash, bash2, csh); Allow .profile_foo etc.
 " Gentoo ebuilds and Arch Linux PKGBUILDs are actually bash scripts
-au BufNewFile,BufRead .bashrc*,bashrc,bash.bashrc,.bash[_-]profile*,.bash[_-]logout*,.bash[_-]aliases*,*.bash,*/{,.}bash[_-]completion{,.d,.sh}{,/*},*.ebuild,*.eclass call SetFileTypeSH("bash")
+au BufNewFile,BufRead .bashrc*,bashrc,bash.bashrc,.bash[_-]profile*,.bash[_-]logout*,.bash[_-]aliases*,*.bash,*/{,.}bash[_-]completion{,.d,.sh}{,/*},*.ebuild,*.eclass,PKGBUILD* call SetFileTypeSH("bash")
 au BufNewFile,BufRead .kshrc*,*.ksh call SetFileTypeSH("ksh")
 au BufNewFile,BufRead */etc/profile,.profile*,*.sh,*.env call SetFileTypeSH(getline(1))