Initially ROOT_BINARY_DIR is automatically generated by CMake and equal
CMAKE_BINARY_DIR. Next change is adjusting ROOT_BINARY_DIR used
in ROOTConfig.cmake for ROOT binaries as a ROOTBIN_DIR

Adding a deprecation for uncorrectly used ROOT_BINARY_DIR

If "^${CMAKE_SOURCE_DIR}" contains special characters, the regular
expression will break with an error like this for Garfield++:

RegularExpression::compile(): Nested *?+.
RegularExpression::compile(): Error in compile.
CMake Error at .../RootNewMacros.cmake:288 (if):
  if given arguments:

    "NOT" "IS_ABSOLUTE" "incdir"
    "OR" "incdir" "MATCHES" "^/<...>/src/Garfield++/HEAD"
    "OR" "incdir" "MATCHES" "^"
    "OR" "incdir" "MATCHES" "^"

  Regular expression
  "^/<...>/src/Garfield++/HEAD"
  cannot compile
Call Stack (most recent call first):
  CMakeLists.txt:118 (ROOT_GENERATE_DICTIONARY)

Also, the (current) build directory is CMAKE_(CURRENT_)BINARY_DIR.
Related Jira issue: ROOT-10210.

CMake should already know which versions of CUDA are required
depending on which standard is being used. The current setup
forbids compiling with C++17 for the host code and C++14 for
CUDA. This will require modifications in TMVA to work, but
relaxing this restriction will at least allow compilation of
ROOT with CUDA and C++17 when it's supported by Nvidia.

Option values *must not be used* before calling the function
ROOT_APPLY_OPTIONS(). This function is responsible for setting
all values using the defaults and what was passed on the command
line, so values before the call are not what the user asked for.

CMake options specified on the command line should not change their
value during configuration. Only default values are allowed to change
(i.e. ${option}_defvalue not ${option}). See ROOT-9385 for more info.

Pere agreed.

Conda sets a prefix for cross-compilation. That prevents CMake from finding headers of
the current ROOT build, see https://sft.its.cern.ch/jira/browse/ROOT-10210 and
https://github.com/conda-forge/root-feedstock/issues/38 . Instead, turn off CMAKE_FIND_ROOT_PATH
for headers searched through relative directories, or absolute ones that start with the
build or source directory. (Do not assume that CURRENT build dir is a subdir of CMAKE_BUILD_DIR.).

The package name in the call to find_package_handle_standard_args()
function must match what is used in the call to find_package() and
the find module name (e.g. FindUnuran.cmake). If there is a mismatch,
then find_package(Unuran REQUIRED) will not cause the desired failure
during configuration when the package is not found. CMake will define
both Unuran_FOUND and UNURAN_FOUND for compatibility reasons.

This option is ported from ROOT 5.x but disabling it makes
compilation break since a long time. Fixes: ROOT-9449.

Use FindPackageHandleStandardArgs.cmake to handle common options
passed to find_package(), like QUIET, REQUIRED, etc.

When builtin_vdt=ON, vdt headers are in ${CMAKE_BINARY_DIR}/include
and libvdt.so is in ${CMAKE_BINARY_DIR}/lib, so we don't need to add
the extra include directory. Once ROOT is installed, the Vdt headers
and library will be along with ROOT ones, so they can also be found
without needing anything else either.

Fixes: ROOT-10197

Python is required by header and manpage generation. However,
since LLVM requires python as well, this only breaks when
configuring with external LLVM/Clang and -Dpython=OFF.

The option fail-on-missing doesn't work when builtins
are enabled by default and not on demand. See ROOT-9385.

This logic is not used anywhere else.

This patch enables TCling to read the Rdict file content from the module file
directly. This is possible because the module file mmaps the Rdict content and
we can create a TMemFile around this blob region.

When we have runtime_cxxmodules on, we do not need to dependency-track the
rdict.pcm files as they do not exist by themselves.