cmake: allow ENABLE_CURLDEBUG=OFF with ENABLE_DEBUG=ON

Before this patch, `ENABLE_CURLDEBUG` (memory tracking) was
unconditionally enabled when `ENABLE_DEBUGBUILD` was set. This made
testing some build configurations complicated. To fix it, this patch
makes `ENABLE_CURLDEBUG` to receive the value of `ENABLE_DEBUG` by
default, while allowing free override by the user.

This allows to use the config:
`ENABLE_DEBUGBUILD=ON ENABLE_CURLDEBUG=OFF`
to enable debug features, without also enabling memory tracking.

This is important because some other build methods allow to set one of
these features but not the other. This patch allows to test any
combination with CMake.

This makes it unnecessary to use the workaround of passing
`-DDEBUGBUILD` via `CMAKE_C_FLAGS`. Which has the disadvantage that our
CMake logic cannot easily detect it, e.g. for disabling symbol hiding on
Windows for `ENABLE_DEBUG`/`DEBUGBUILD` builds.

Cherry-picked from #13718
Closes #13792

CMakeLists.txt

@@ -113,14 +113,13 @@ cmake_dependent_option(ENABLE_THREADED_RESOLVER "Set to ON to enable threaded DN
         ON "NOT ENABLE_ARES"
         OFF)
 
-option(ENABLE_DEBUG "Set to ON to enable curl debug features" OFF)
-option(ENABLE_CURLDEBUG "Set to ON to build with TrackMemory feature enabled" OFF)
-
 include(PickyWarnings)
 
+option(ENABLE_DEBUG "Set to ON to enable curl debug features" OFF)
+option(ENABLE_CURLDEBUG "Set to ON to build with TrackMemory feature enabled" ${ENABLE_DEBUG})
+
 if(ENABLE_DEBUG)
   set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS DEBUGBUILD)
-  set(ENABLE_CURLDEBUG ON)
 endif()
 
 if(ENABLE_CURLDEBUG)

appveyor.sh

@@ -43,7 +43,7 @@ if [ "${BUILD_SYSTEM}" = 'CMake' ]; then
   [ "${PRJ_CFG}" = 'Release' ] && options+=' -DCMAKE_RUNTIME_OUTPUT_DIRECTORY_RELEASE='
   [[ "${PRJ_GEN}" = *'Visual Studio'* ]] && options+=' -DCMAKE_VS_GLOBALS=TrackFileAccess=false'
   if [ "${PRJ_GEN}" = 'Visual Studio 9 2008' ]; then
-    [ "${DEBUG}" = 'ON' ] && [ "${SHARED}" = 'ON' ] && SKIP_RUN='Crash on startup in -DDEBUGBUILD shared builds'
+    [ "${DEBUG}" = 'ON' ] && [ "${SHARED}" = 'ON' ] && SKIP_RUN='Crash on startup in ENABLE_DEBUG=ON shared builds'
     # Fails to run without this due to missing MSVCR90.dll / MSVCR90D.dll
     options+=' -DCURL_STATIC_CRT=ON'
   fi