When using builtin_openssl=ON, CMake erroneously exports the builtin
static libraries in ROOTConfig-targets.cmake, which causes problems with
dependent projects. In order to avoid this, we need Net and RHTTP to use
SSL as a private dependency. Since CMake requires target_link_libraries()
to either be all-plain (as before) or all-keyword (required to allow
PRIVATE linking), we need to move the build system to use all-keyword
linking only.

Fixes: ROOT-9532

Addresses ROOT-9311

There is also no longer the need to add BUILTINS OPENSSL
to targets linking with the builtin version.

To link against rpdutil one also needs ${CRYPTLIBS}, so the rpdutil
target should propagate that to libraries linking against it via the
INTERFACE_LINK_LIBRARIES property, instead of adding ${CRYPTLIBS} to all
libraries linking against rpdutil.

We remove ${CMAKE_DL_LIBS} from the dependencies, since it is now in
${OPENSSL_LIBRARIES} for the builtin openssl, as it is required by
libssl. It would be nice to also use target_compile_definitions instead
of simply add_definitions, but because ROOT_STANDARD_LIBRARY_PACKAGE
does dictionary generation when it's called, it doesn't work.

These are temporary static libraries that need to be linked to a
final shared library, so they must be compiled with -fPIC.

One should always enable _GNU_SOURCE to use extra functionality from
glibc

THttpServer::SetTerminate() should only be used when really terminating
application. In such mode connections and websockets not cleaned up
properly

Signed-off-by: Olivier Couet <olivier.couet@gmail.com>

target

Now all these classes defined in http library internally

Was used to implement text-based CEF messaging, which is not efficient

Set ownership and websocket ID directly in that method

It is small sub-class, which allows to start http server like: 

    new THttpServer("https:4567?ssl_cert=certificate.pem");

Certificate should be provided in any case

This include directory is now added automatically by the imported
target for Davix.

OpenSSL needs -ldl, but does not propagate that properly, so
when linked statically into Davix, there are missing symbols:

builtins/davix/DAVIX-prefix/lib/libdavix.a(davixcontext.cpp.o):
	In function `Davix::LibPath::LibPath()':
builtins/davix/DAVIX-prefix/src/DAVIX/src/davixcontext.cpp:154:
	undefined reference to `dladdr'
builtins/openssl/OPENSSL-prefix/lib/libcrypto.a(dso_dlfcn.o):
	In function `dlfcn_globallookup':
dso_dlfcn.c:(.text+0x11): undefined reference to `dlopen'
dso_dlfcn.c:(.text+0x24): undefined reference to `dlsym'
dso_dlfcn.c:(.text+0x2f): undefined reference to `dlclose'

Therefore we need to add ${CMAKE_DL_LIBS} to the Davix::Davix
imported target so that -ldl gets added when linking to Davix.
We can then remove the ${SYSLIBS} from RDAVIX, which had this
role before.

In some builds calling find_package(PkgConfig) more than once fails
with an error like the one below:

-- Checking for module 'davix>=0.6.4'
--   Found davix, version 0.6.7
...
-- Checking for module 'davix>=0.6.4'
--
CMake Error at [...]/share/cmake-3.7/Modules/FindPkgConfig.cmake:415 (message):
  A required package was not found
Call Stack (most recent call first):
  [...]/share/cmake-3.7/Modules/FindPkgConfig.cmake:588 (_pkg_check_modules_internal)
  cmake/modules/FindDavix.cmake:61 (pkg_check_modules)
  cmake/modules/SearchInstalledSoftware.cmake:9 (_find_package)
  net/davix/CMakeLists.txt:6 (find_package)

-- Configuring incomplete, errors occurred!

This is necessary to allow builtin_openssl option to work by linking
OpenSSL statically and not distributing any headers afterwards.

If any SSL-related defines appeared in civetweb (even which says - do
not load SSL), civetweb starts to include ssl headers

Seems to be, Windows has a problem when many definitions combined
together

dependencies