xbps-src: reduce basename(1) usage.

This saves a few exec()s.

xbps-src

@@ -1,6 +1,8 @@
 #!/bin/bash
 # vim: set ts=4 sw=4 et:
 
+readonly PROGNAME="${0##*/}"
+
 print_cross_targets() {
     local f
     for f in common/cross-profiles/*.sh; do
@@ -10,7 +12,7 @@ print_cross_targets() {
 
 usage() {
     cat << _EOF
-$(basename $0): [options] <target> [arguments]
+$PROGNAME: [options] <target> [arguments]
 
 Targets: (only one may be specified)
 
@@ -380,14 +382,10 @@ exit_func() {
     exit 2
 }
 
-basename_cwd() {
-    echo $(basename $(pwd))
-}
-
 read_pkg() {
     if [ -z "${XBPS_TARGET_PKG}" ]; then
         [ ! -r ./template ] && msg_error "missing build template in $(pwd).\n"
-        XBPS_TARGET_PKG=$(basename_cwd)
+        XBPS_TARGET_PKG=${PWD##*/}
     fi
     setup_pkg "$XBPS_TARGET_PKG" "$XBPS_CROSS_BUILD" "$1"
 }