Update on "Install libcpp from release package other than apt-get"

A few changes

1. Use the release package from https://releases.llvm.org/ to install libcpp, so we can install from different linux in addition to Ubuntu
2. Seperate out the qnn version and the url to a seperate file, for better versin management in the future

Differential Revision: [D77048745](https://our.internmc.facebook.com/intern/diff/D77048745/)

Differential Revision: [D77048745](https://our.internmc.facebook.com/intern/diff/D77048745)

[ghstack-poisoned]

Author: cccclai

.ci/scripts/setup-qnn-deps.sh

@@ -7,7 +7,7 @@
 
 set -ex
 
-source "$(dirname "${BASH_SOURCE[0]}")/../../../backends/qualcomm/scripts/install_qnn_sdk.sh"
+source "$(dirname "${BASH_SOURCE[0]}")/../../backends/qualcomm/scripts/install_qnn_sdk.sh"
 
 setup_libcpp 12
 install_qnn