package/glog: needs gcc >= 6

C++14 is mandatory since bump to version 0.7.0 in commit
2e9f161d4a7a68a041860e5855e98bee9d3a1498 and
https://github.com/google/glog/commit/674283420118bb919f83ceb3d9dee31ef43ff3aa
and
https://github.com/google/glog/commit/42a185cd888439d500a35191cd31a605b7c5bd20
resulting in the following build failure with gcc 5:

In file included from /home/buildroot/autobuild/run/instance-2/output-1/build/glog-0.7.0/src/demangle.cc:43:0:
/home/buildroot/autobuild/run/instance-2/output-1/build/glog-0.7.0/src/utilities.h:210:22: error: enclosing class of constexpr non-static member function 'google::glog_internal_namespace_::FileDescriptor::operator bool() const' is not a literal type
   constexpr explicit operator bool() const noexcept {
                      ^

Fixes: 2e9f161d4a7a68a041860e5855e98bee9d3a1498
 - http://autobuild.buildroot.org/results/8d5e105283ead1057545b46726385f4ba4dff29e

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/glog/Config.in

@@ -2,11 +2,13 @@ config BR2_PACKAGE_GLOG
 	bool "glog"
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_TOOLCHAIN_HAS_THREADS
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_6 # C++14
 	help
 	  C++ implementation of the Google logging module
 
 	  https://github.com/google/glog
 
-comment "glog needs a toolchain w/ C++, threads"
+comment "glog needs a toolchain w/ C++, threads, gcc >= 6"
 	depends on !BR2_INSTALL_LIBSTDCPP || \
-		!BR2_TOOLCHAIN_HAS_THREADS
+		!BR2_TOOLCHAIN_HAS_THREADS || \
+		!BR2_TOOLCHAIN_GCC_AT_LEAST_6

package/opencv4-contrib/Config.in

@@ -251,6 +251,7 @@ config BR2_PACKAGE_OPENCV4_CONTRIB_LIB_SALIENCY
 
 config BR2_PACKAGE_OPENCV4_CONTRIB_LIB_SFM
 	bool "sfm"
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_6 # glog
 	select BR2_PACKAGE_OPENCV4_LIB_IMGPROC
 	select BR2_PACKAGE_OPENCV4_LIB_IMGCODECS
 	select BR2_PACKAGE_EIGEN
@@ -261,6 +262,9 @@ config BR2_PACKAGE_OPENCV4_CONTRIB_LIB_SFM
 	  to perform 3d reconstruction from 2d images. The core of
 	  the module is a light version of Libmv.
 
+comment "sfm needs a toolchain w/ gcc >= 6"
+	depends on !BR2_TOOLCHAIN_GCC_AT_LEAST_6
+
 config BR2_PACKAGE_OPENCV4_CONTRIB_LIB_SHAPE
 	bool "shape"
 	help