hooks/gen-provides: Correctly uses builtin provides and mapfile

- `read -r -a' somehow doesn't work with newline, but we don't need to
  invoke a builtin for that, we can just simply assign to the variable
- In `mapfile', `-t' is used for removing newline, not for target. The
  targeting array need to be specified last in the array.

Close #53532

common/hooks/pre-pkg/04-generate-provides.sh

@@ -1,4 +1,4 @@
-# vim: set ts=4 sw=4 et:
+# vim: set ts=4 sw=4 ft=bash et:
 #
 # This hook executes the following tasks:
 #	- Generates provides file with provides entries for xbps-create(1)
@@ -14,13 +14,11 @@ generate_python_provides() {
 }
 
 hook() {
-    local -a _provides=()
-
     # include explicit values from the template
-    read -r -a _provides <<< "$provides"
+    local -a _provides=($provides)
 
     # get the canonical python package names for each python module
-    mapfile -t _provides -O "${#_provides[@]}" < <( generate_python_provides )
+    mapfile -t -O "${#_provides[@]}" _provides < <( generate_python_provides )
 
     if [ "${#_provides[@]}" -gt 0 ]; then
         echo "   ${_provides[*]}"