ext: test: Split up the GTEST_CPPFLAGS and CPPFLAGS.

scons seems to get confused in some situations when this is a single
large string and passes it as one big argument to g++ instead of
breaking it up into several arguments.

We need to do the work for it and break it into individual arguments,
like what was already being done with GTEST_LIBS.

Also wrap some overly long lines.

Change-Id: Ib7688a7abced43a9c62994d17b78d358fc0dc000
Reviewed-on: https://gem5-review.googlesource.com/c/16567
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

ext: Build googlemock with googletest

googlemock needs to be built together with googletest. This patch
is enabling it by doing the following things

* Moving googletest and googlemock under the same top level directory,
so that we have a single SConscript for building them.
This also matches googletest directory structure:
googletest
|_googletest
|_googlemock

* Adding a shared SConscript which is building gmock and gtest as libgtest
* Removing googletest/SConscript

Change-Id: I88accbdd2e80fb47efaa17819233371fbad6acaa
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/14696
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

tests: scons: Integrate the googletest library into the build.

A static library is built using gtest-all.cc and includes the gtest
main function from gtest_main.cc. extra libraries to use when linking
are included in the main environment variable GTEST_LIBS, and extra
CPPFLAGS are in GTEST_CPPFLAGS. The library's path is added to the
library search path, and it's headers to the header search path.

Change-Id: I2bd6f705bd9fac5db9280996f574b168c11ff8ce
Reviewed-on: https://gem5-review.googlesource.com/6083
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>