build: Rename PACKAGE_* variables to CLIENT_*

The use of `PACKAGE_NAME` for the project's variable name is
problematic, as this name is commonly used in CMake's interface
variables. If third-party CMake code handles with scopes improperly,
our `PACKAGE_NAME` variable could end up with an unexpected value.

This change avoids such conflicts by renaming all `PACKAGE_*` variables
to `CLIENT_*`.

CMakeLists.txt

@@ -16,7 +16,7 @@ endif()
 #=============================
 # Project / Package metadata
 #=============================
-set(PACKAGE_NAME "Bitcoin Core")
+set(CLIENT_NAME "Bitcoin Core")
 set(CLIENT_VERSION_MAJOR 28)
 set(CLIENT_VERSION_MINOR 99)
 set(CLIENT_VERSION_BUILD 0)
@@ -47,14 +47,14 @@ project(BitcoinCore
   LANGUAGES NONE
 )
 
-set(PACKAGE_VERSION ${PROJECT_VERSION})
+set(CLIENT_VERSION_STRING ${PROJECT_VERSION})
 if(CLIENT_VERSION_RC GREATER 0)
-  string(APPEND PACKAGE_VERSION "rc${CLIENT_VERSION_RC}")
+  string(APPEND CLIENT_VERSION_STRING "rc${CLIENT_VERSION_RC}")
 endif()
 
 set(COPYRIGHT_HOLDERS "The %s developers")
-set(COPYRIGHT_HOLDERS_FINAL "The ${PACKAGE_NAME} developers")
-set(PACKAGE_BUGREPORT "https://github.com/bitcoin/bitcoin/issues")
+set(COPYRIGHT_HOLDERS_FINAL "The ${CLIENT_NAME} developers")
+set(CLIENT_BUGREPORT "https://github.com/bitcoin/bitcoin/issues")
 
 #=============================
 # Language setup