install_deps.sh: fix (hopefully) broken OSL building on modern RPM-like distro.

Those stupid ones only have one version of llvm (obviously not 3.4 one ;) ), so we have to build again
LLVM3.4 in those cases. Thing is,
* I did not update LLVM magic number when fixed a stupid typo breaking OSL building (the terminfo thing),
  so many people were still using previously-built LLVM.
* Even worse, options passed to OSL to specify own LLVM from /opt/lib were wrong (not sure when this got
  out of sync...).

Thanks to mib2berlin and slikdigit for the report & testings!

build_files/build_environment/install_deps.sh

@@ -1527,7 +1527,7 @@ clean_LLVM() {
 
 compile_LLVM() {
   # To be changed each time we make edits that would modify the compiled result!
-  llvm_magic=2
+  llvm_magic=3
   _init_llvm
 
   # Clean install if needed!
@@ -1700,7 +1700,7 @@ compile_OSL() {
     if [ ! -z $LLVM_VERSION_FOUND ]; then
       cmake_d="$cmake_d -D LLVM_VERSION=$LLVM_VERSION_FOUND"
       if [ -d $INST/llvm ]; then
-        cmake_d="$cmake_d -D LLVM_ROOT_DIR=$INST/llvm"
+        cmake_d="$cmake_d -D LLVM_DIRECTORY=$INST/llvm"
         cmake_d="$cmake_d -D LLVM_STATIC=ON"
       fi
     fi