Drishti does not compile with linux gcc anymore.

[GORGES]

When compiling for toolchain "gcc" on a linux box, this error is raised:

src/lib/drishti/core/Logger.cpp:52:38: error: ‘stdout_sink_mt’ is not a member of ‘spdlog::sinks’

I suspect that the GCC libraries have evolved, or perhaps an include file is missing.

[ruslo]

I can't compile with GCC too but the error is different.

For the record GCC is not a part of CI testing (note: GCC is a default compiler, so here we use GCC too: https://github.com/elucideye/drishti#generate-and-build)

CI is tested with Clang 5.0:

• https://travis-ci.org/elucideye/drishti/jobs/486975559

I have tried Clang 5.0.2, 7.0.1 and 8.0.0 without success. The error is in 'ogles_gpgpu' package.

E.g. for Clang 5.0.2:

In file included from /.../Build/ogles_gpgpu/Source/ogles_gpgpu/common/proc/multipass/gauss_opt_pass.cpp:13:
/.../clang+llvm-5.0.2-x86_64-linux-gnu-ubuntu-16.04/bin/../include/c++/v1/cmath:313:9:
  error: no member named 'signbit' in the global namespace; did you mean '__signbit'?
using ::signbit;
      ~~^