Update ./configure to detect ninja package of debian/ubuntu (#4)

configure

@@ -8,27 +8,40 @@ cont() {
     fi
 }
 
-if [ ! -e `which cmake` ]
+if [ ! -x "$(which cmake 2>/dev/null)" ]
 then
-  echo "CMake required."
+  echo "-!- CMake required."
   exit 1
 fi
 
-if [ -x "$(which ninja 2>/dev/null)" ]; then
-  echo "-- Found Ninja: $(which ninja)"
+ninja_bin="$(which ninja-build 2>/dev/null)"
+if ! [ -x "$ninja_bin" ]; then
+  ninja_bin="$(which ninja 2>/dev/null)"
+fi
+if [ -x "$ninja_bin" ]; then
+  ninja_version=$($ninja_bin --version 2>/dev/null)
+  if [ $? -eq 0 ]; then
+    echo "-- Found Ninja: $ninja_bin (found version \"$ninja_version\")"
     cmake_type="Ninja"
-  exec_bin="ninja"
-elif [ -x "$(which ninja-build 2>/dev/null)" ]; then
-  echo "-- Found Ninja: $(which ninja-build)"
-  cmake_type="Ninja"
-  exec_bin="ninja-build"
-elif [ -x "$(which make 2>/dev/null)" ]; then
-  echo "-- Found Make: $(which make)"
+    exec_bin="$ninja_bin"
+    exec_command="$exec_bin"
+  elif [[ "/usr/sbin/ninja" == "$ninja_bin" ]]; then
+    echo "-- Ninja at $ninja_bin is not usable. Did you install 'ninja' instead of 'ninja-build'?"
+  fi
+fi
+
+if ! [ -x "$exec_bin" ]; then
+  make_bin="$(which make 2>/dev/null)"
+  if [ -x "$make_bin" ]; then
+    echo "-- Found Make: $make_bin"
+    echo "--   Using Ninja (ninja-build) might improve build experience."
     cmake_type="Unix Makefiles"
-  exec_bin="make -j4"
-  echo "--   Using Ninja might improve build experience."
-  cont
-else
+    exec_bin="$make_bin"
+    exec_command="$exec_bin -j4"
+  fi
+fi
+
+if ! [ -x "$exec_bin" ]; then
   echo "-!- No compatible build system (Ninja, Make) found."
   exit 4
 fi
@@ -66,9 +79,9 @@ if [ "$cmake_type" == "Ninja" ]
 then
 cat << EOF > Makefile
 default:
-	@sh -c "$exec_bin"
+	@sh -c "$exec_command"
 %:
-	@sh -c "$exec_bin \"\$@\""
+	@sh -c "$exec_command \"\$@\""
 EOF
 fi
 
@@ -76,7 +89,7 @@ cd ..
 
 cat << EOF > Makefile
 default:
-	@sh -c "cd build; $exec_bin"
+	@sh -c "cd build; $exec_command"
 %:
-	@sh -c "cd build; $exec_bin \"\$@\""
+	@sh -c "cd build; $exec_command \"\$@\""
 EOF