fix bug of freetype2 build for ffmpeg, depends on pkg-config

@@ -70,6 +70,7 @@ else
 fi
 
 # freetype-2.4.0
+# remark: we must ensure the pkg-config tool installed.
 if [[ -f ${ff_release_dir}/lib/libfreetype.a ]]; then
     echo "libfreetype is ok"
 else

@@ -102,6 +102,14 @@ function Ubuntu_prepare()
             sudo apt-get install -y --force-yes zlib1g-dev; ret=$?; if [[ 0 -ne $ret ]]; then return $ret; fi
             echo "install zlib1g-dev success"
         fi
+        
+        # for freetype2
+        pkg-config --help >/dev/null 2>&1; ret=$?; if [[ 0 -ne $ret ]]; then
+            echo "install pkg-config"
+            require_sudoer "sudo apt-get install -y --force-yes pkg-config"
+            sudo apt-get install -y --force-yes pkg-config; ret=$?; if [[ 0 -ne $ret ]]; then return $ret; fi
+            echo "install pkg-config success"
+        fi
     fi
     
     # for arm, install the cross build tool chain.
@@ -202,6 +210,14 @@ function Centos_prepare()
             sudo yum install -y zlib-devel; ret=$?; if [[ 0 -ne $ret ]]; then return $ret; fi
             echo "install zlib-devel success"
         fi
+    
+        # for freetype2
+        pkg-config --help >/dev/null 2>&1; ret=$?; if [[ 0 -ne $ret ]]; then
+            echo "install pkg-config"
+            require_sudoer "sudo yum install -y pkg-config"
+            sudo yum install -y pkg-config; ret=$?; if [[ 0 -ne $ret ]]; then return $ret; fi
+            echo "install pkg-config success"
+        fi
     fi
     
     # for arm, install the cross build tool chain.