Delete entire $srcdir upon clean build

Currently, the file glob used to clean the $srcdir misses dotfiles.

This commit instead removes the directory entirely and recreates it.
Since the directory has to exist prior to deletion, the creation commands
are duplicated. Perhaps they could be moved to a function later on.

The directory cannot be removed while inside it, so the directory change
is moved down the line. One important insight here is that almost all functions
after it are actually independent of $pwd, allowing the optimization of just
not changing directory. They do however depend on the existence of $srcdir, so
it has to be recreated.
The only exception to this is `extract_sources` which depends on $pwd being $srcdir.

An alternative proposal wanted to extend the file matching for deletion, but it
was deemed impractical.

scripts/makepkg.sh.in

@@ -1334,10 +1334,9 @@ else
 	fi
 fi
 
-# get back to our src directory so we can begin with sources
+# ensure existence of our src directory so we can begin with sources
 mkdir -p "$srcdir"
 chmod a-s "$srcdir"
-cd_safe "$srcdir"
 
 if (( !REPKG )); then
 	if (( NOEXTRACT && ! VERIFYSOURCE )); then
@@ -1349,9 +1348,12 @@ if (( !REPKG )); then
 
 		if (( CLEANBUILD )); then
 			msg "$(gettext "Removing existing %s directory...")" "\$srcdir/"
-			rm -rf "$srcdir"/*
+			rm -rf "$srcdir"
+			mkdir -p "$srcdir"
+			chmod a-s "$srcdir"
 		fi
 
+		cd_safe "$srcdir"
 		extract_sources
 		if (( PREPAREFUNC )); then
 			run_prepare