Recompilation fixes

[ok-nick]

libcec-sys recompiles every time due to an incorrect path to the build script for rerun-if-changed. This should fix it.

[ssalonen]

Thanks! Good find. The build used to be in the root of the project, apparently forgot to update this after the move.

Noticed that it is also otherwise

Would you please

• add vendor folder as well to trigger a rebuild
• add additional env variables that affect the build (good overview in https://cmake.org/cmake/help/latest/manual/cmake-env-variables.7.html and https://crates.io/crates/cc)

  println!("cargo:rerun-if-env-changed=LD_LIBRARY_PATH");
  println!("cargo:rerun-if-env-changed=LDFLAGS");
  println!("cargo:rerun-if-env-changed=PATH");
  println!("cargo:rerun-if-env-changed=PKG_CONFIG_PATH");
  println!("cargo:rerun-if-env-changed=CC");
  println!("cargo:rerun-if-env-changed=CFLAGS");
  println!("cargo:rerun-if-env-changed=CXX");
  println!("cargo:rerun-if-env-changed=CXXFLAGS");

• add a change log entry

[ssalonen]

Thank you!