CMake: fix warning with external googletest

[rouault]

Recent CMake versions throw the following warning when building
googletest 1.8.1. Bumping to 1.11.0 that has a minimum version of 2.8.12
fixes that

 CMake Deprecation Warning at build/googletest-src/CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 2.8.12 will be removed from a future version of
  CMake.

[rouault]

bummer: gcc 4.8 is not able to build googletest 1.11.0

[kbevers]

bummer: gcc 4.8 is not able to build googletest 1.11.0

Maybe it's time to move on? Most recent GCC 4.8 version is from 2015

[rouault]

Maybe it's time to move on? Most recent GCC 4.8 version is from 2015

yeah, I'm changing this conf to use the default GCC 5.4 from Ubuntu 16.04

[mwtoews]

If we really want to keep GCC 4.8 in the mix, another strategy is to edit test/googletest/CMakeLists.txt.in with something like:

if(CMAKE_VERSION VERSION_LESS 3.???)
  # GCC 4.8 compat
else()
  # more recent compat
endif()

[rouault]

If we really want to keep GCC 4.8 in the mix, another strategy is to edit test/googletest/CMakeLists.txt.in with something like:

I don't have any personal interest in such old versions.
I don't see the relationship between the CMake version and the GCC version. A system with gcc 4.8 has normally not CMake >= 3.9 by default, so they should use a backport version, which can be anything >= 3.9

[mwtoews]

Yup, lets move on from GCC 4.8. While interesting to see it raise different issues in the CI compared to newer compilers, it's really a bit of a distraction. GCC 5.4 is from 2016, so a bit newer. Nevertheless, I'd like to see the CMake warning go away with the upgraded googletest.