buildsystem: make get-vlc.sh work from any directories

buildsystem/get-vlc.sh

 #! /bin/sh
 set -e
 
+readonly SCRIPT_DIR="$(cd "$(dirname "$0")" ; pwd -P)"
+
 #############
 # FUNCTIONS #
 #############
@@ -70,6 +72,7 @@ done
 VLC_TESTED_HASH=488ee616e5c94e516563095c6b3ac3a85cf72871
 VLC_REPOSITORY=https://code.videolan.org/videolan/vlc.git
 VLC_BRANCH=master
+VLC_PATCHES=${SCRIPT_DIR}/../libvlc/patches
 if [ ! -d "vlc" ]; then
     diagnostic "VLC sources: not found, cloning"
     git clone "${VLC_REPOSITORY}" vlc -b ${VLC_BRANCH} --single-branch || fail "VLC sources: git clone failed"
@@ -78,7 +81,7 @@ if [ ! -d "vlc" ]; then
     git reset --hard ${VLC_TESTED_HASH} || fail "VLC sources: VLC_TESTED_HASH ${VLC_TESTED_HASH} not found"
     diagnostic "VLC sources: applying custom patches"
     # Keep Message-Id inside commits description to track them afterwards
-    git am --message-id ../libvlcjni/libvlc/patches/*.patch || fail "VLC sources: cannot apply custom patches"
+    git am --message-id ${VLC_PATCHES}/*.patch || fail "VLC sources: cannot apply custom patches"
     cd ..
 else
     diagnostic "VLC source: found sources, leaving untouched"
@@ -88,7 +91,7 @@ if [ "$BYPASS_VLC_SRC_CHECKS" = 1 ]; then
 elif [ $RESET -eq 1 ]; then
     cd vlc
     git reset --hard ${VLC_TESTED_HASH} || fail "VLC sources: VLC_TESTED_HASH ${VLC_TESTED_HASH} not found"
-    for patch_file in ../libvlcjni/libvlc/patches/*.patch; do
+    for patch_file in ${VLC_PATCHES}/*.patch; do
         git am --message-id $patch_file
         check_patch_is_applied "$patch_file"
     done
@@ -99,7 +102,7 @@ else
     cd vlc
     git cat-file -e ${VLC_TESTED_HASH} 2> /dev/null || \
         fail "Error: Your vlc checkout does not contain the latest tested commit: ${VLC_TESTED_HASH}"
-    for patch_file in ../libvlcjni/libvlc/patches/*.patch; do
+    for patch_file in ${VLC_PATCHES}/*.patch; do
         check_patch_is_applied "$patch_file"
     done
     cd ..