faster strip_files() function

Tested with a port with 5500 output files, from which 53 candidates
for stripping. The timing was:
	- 30  secs (old code)
	- 0.2 secs (new code - current patch)
	- 1.4 secs (new code with proper quoting - not commited)

Most of the time is spent in getting the output from the file program.

The old code started the file program for every file.

The new/present code starts N=$(nproc) processes in parallel with 10 input
files for each 'file' process. The output of the file program is feed
to an awk process which filters-out only the candidates for stripping.
This process runs in parallel too (but with one file per strip process).

The --no-buffer options is used because it sounds good (the strip should
start as soon as one of the file processes has a verdict for one of
their 10 files), but I didn't measure it.

The "xargs -r -L10 -P$N" command will miss the files with spaces.
For a file named "a b" it will spawn:
	file "a" "b"
A slower version, with proper quoting, "xargs -r -L1 -P$N -I{} file ... '{}'",
will spawn:
	file "a b"

* xargs will force -L1 if -I{} is used

Given that the file process doesn't return error codes for non-existing
files, and that there is a very low probability that we have ports with
filenames constaining spaces that are worth stripping them, I choose to
keep the faster (non perfect) version.

pkgmk.in

@@ -409,7 +409,8 @@ refresh_signature() {
 }
 
 strip_files() {
-	local FILE FILTER
+	local FILTER
+	local N=$(nproc)
 
 	cd $PKG
 
@@ -419,18 +420,18 @@ strip_files() {
 		FILTER="cat"
 	fi
 
-	find . -type f -printf "%P\n" | $FILTER | while read FILE; do
-		case $(file -b "$FILE") in
-		*ELF*executable*not\ stripped*)
-			strip --strip-all "$FILE"
-			;;
-		*ELF*shared\ object*not\ stripped*)
-			strip --strip-unneeded "$FILE"
-			;;
-		current\ ar\ archive)
-			strip --strip-debug "$FILE"
-		esac
-	done
+	find . -type f -printf "%P\n" | $FILTER                   \
+		| xargs -r -L10 -P$N                              \
+			file --no-buffer --separator '>'          \
+			-e apptype -e ascii -e encoding -e tokens \
+			-e cdf -e compress -e tar -e text         \
+		| awk '
+			BEGIN { FS = ">[ ]+" }
+			$0 ~ /ELF.*executable.*not stripped/    { print "--strip-all      \"" $1 "\"" }
+			$0 ~ /ELF.*shared object.*not stripped/ { print "--strip-unneeded \"" $1 "\"" }
+			$2 == "current ar archive"              { print "--strip-debug    \"" $1 "\"" }
+			' \
+		| xargs -r -L1 -P$N strip
 }
 
 compress_manpages() {