common/hooks: speed up generate-runtime-deps.

Instead of using file(1) to check for ELF files, just read bytes
directly from the file and check if they are the ELF magic bytes.

Should probably be factored out into a common function that can be used
in other places, if necessary.

Also use awk instead of "grep|awk" for some minor speedup.

common/hooks/pre-pkg/04-generate-runtime-deps.sh

@@ -47,7 +47,7 @@ store_pkgdestdir_rundeps() {
 }
 
 hook() {
-    local depsftmp f lf j mapshlibs sorequires _curdep
+    local depsftmp f lf j mapshlibs sorequires _curdep elfmagic
 
     # Disable trap on ERR, xbps-uhelper cmd might return error... but not something
     # to be worried about because if there are broken shlibs this hook returns
@@ -72,18 +72,17 @@ hook() {
 		    msg_normal "Skipping dependency scan for ${lf}\n"
 		    continue
 	    fi
-        case "$(file -bi "$f")" in
-            application/x-*executable*|application/x-sharedlib*)
-                for nlib in $($OBJDUMP -p "$f"|grep NEEDED|awk '{print $2}'); do
-                    [ -z "$verify_deps" ] && verify_deps="$nlib" && continue
-                    found=0
-                    for j in ${verify_deps}; do
-                        [[ $j == $nlib ]] && found=1 && break
-                    done
-                    [[ $found -eq 0 ]] && verify_deps="$verify_deps $nlib"
+        read -n4 elfmagic < "$f"
+        if [ "$elfmagic" = $'\177ELF' ]; then
+            for nlib in $($OBJDUMP -p "$f"|awk '/NEEDED/{print $2}'); do
+                [ -z "$verify_deps" ] && verify_deps="$nlib" && continue
+                found=0
+                for j in ${verify_deps}; do
+                    [[ $j == $nlib ]] && found=1 && break
                 done
-                ;;
-        esac
+                [[ $found -eq 0 ]] && verify_deps="$verify_deps $nlib"
+            done
+        fi
     done
     exec 0<&3 # restore stdin
     rm -f $depsftmp