toolchain/wrapper: replace legacy backticks with $()

This replaces deprecated backticks by more versatile $(...) syntax.

Found with shellcheck.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
[alter commit title, extend commit message]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/toolchain/files/wrapper.sh

@@ -15,10 +15,10 @@
 #
 
 PROGNAME=$0
-REALNAME=`readlink -f $0`
+REALNAME=$(readlink -f $0)
 
-REALNAME_BASE=`basename $REALNAME`
-REALNAME_DIR=`dirname $REALNAME`
+REALNAME_BASE=$(basename $REALNAME)
+REALNAME_DIR=$(dirname $REALNAME)
 
 TARGET_FUNDAMENTAL_ASFLAGS=''
 TARGET_FUNDAMENTAL_CFLAGS=''