signlk.sh: use make -C instead of shell variable

Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>

signer/Makefile

 CXX=g++
-cur-dir   :=  $(mfile_path)
+cur-dir   :=  $(shell pwd)
 ELFIODIR=${cur-dir}/ELFIO/elfio/
 SOURCES=${cur-dir}/signlk.cpp 
 CPPFLAGS=-c -Wall -std=c++0x -I$(cur-dir)/ELFIO/

signlk.sh

@@ -108,8 +108,7 @@ if [ ! "$(g++ --version)" ]; then
    exit 8
 fi
 
-export mfile_path=$DIR/signer
-make -f $mfile_path/Makefile
+make -C $DIR/signer
 
 if [ "$?" != 0 ]; then
     echo " failed to build executable"