Fix CMAKE_INSTALL_PREFIX to respect user-specified values

The previous code unconditionally set CMAKE_INSTALL_PREFIX, which
overrode any command-line -DCMAKE_INSTALL_PREFIX=... settings.
This caused Docker builds to install to the wrong directory.

Now uses CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT to only set
the default when the user hasn't specified a custom install prefix.

Author: RahulHere

CMakeLists.txt

@@ -83,8 +83,10 @@ if(NOT CMAKE_BUILD_TYPE)
     set(CMAKE_BUILD_TYPE Debug)
 endif()
 
-# Set custom install prefix
-set(CMAKE_INSTALL_PREFIX "${CMAKE_CURRENT_SOURCE_DIR}/install_prefix_dir")
+# Set custom install prefix (only if not specified by user)
+if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+    set(CMAKE_INSTALL_PREFIX "${CMAKE_CURRENT_SOURCE_DIR}/install_prefix_dir" CACHE PATH "Install prefix" FORCE)
+endif()
 
 #Compiler flags
 if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")