makepkg: normalize whitespace in $pkgdesc when writing .PKGINFO

Specifically, we shouldn't allow newlines in the pkgdesc field, as
pacman will ignore the continuation and end the description prematurely
as written to the local DB. Normalize ALL whitespace, replacing it with
single whitespace characters.

Fixes strange errors as seen by FS#32852.

Signed-off-by: Dave Reisner <dreisner@archlinux.org>
Signed-off-by: Allan McRae <allan@archlinux.org>

scripts/makepkg.sh.in

@@ -1721,7 +1721,7 @@ write_pkginfo() {
 	printf "pkgname = %s\n" "$pkgname"
 	(( SPLITPKG )) && echo pkgbase = $pkgbase
 	echo "pkgver = $(get_full_version)"
-	printf "pkgdesc = %s\n" "$pkgdesc"
+	printf "pkgdesc = %s\n" "${pkgdesc//+([[:space:]])/ }"
 	printf "url = %s\n" "$url"
 	printf "builddate = %s\n" "$builddate"
 	printf "packager = %s\n" "$packager"