Technical Debt: Linux doesn't build in C++17

[greenfire27]

C++17 is our target version of C++. Linux (using makefile) is currently at C++14.

[elementc]

While writing #43, a fix for #42, I bumped us from -std=gnu++11 to -std=c++14.

I tried to go as far as -std=c++17, but came up short due to this build error:

make: *** [Torque2D.mk:130: Debug/2d/gui/guiSpriteCtrl.cc.o] Error 1
In file included from ../../source/assets/assetManager.h:31,
                 from ../../source/assets/assetPtr.h:27,
                 from ../../source/2d/assets/AnimationAsset.h:27,
                 from ../../source/2d/core/ImageFrameProviderCore.h:31,
                 from ../../source/2d/core/ImageFrameProvider.h:27,
                 from ../../source/2d/core/ImageFrameProvider.cc:23:
../../source/persistence/taml/taml.h:88:13: error: 'HashMap' does not name a type
   88 |     typedef HashMap<SimObjectId, TamlWriteNode*>    typeCompiledHash;
      |             ^~~~~~~
compilation terminated due to -Wfatal-errors.

Which is vaguely ironic since switching to HashMap from std::unordered_map was the fix for #42. Alas, there's some work to go to overcome this one.

For Linux builds, we control the C++ standard via these lines:

Torque2D/engine/compilers/Make-32bit/Torque2D.mk

Line 68 in ee345f3

CFLAGS := -std=c++14 -MMD -I. -Wfatal-errors -Wunused -m32 -msse -march=i686 -pipe

Torque2D/engine/compilers/Make-64bit/Torque2D.mk

Line 66 in ee345f3

CFLAGS := -std=c++14 -MMD -I. -Wfatal-errors -Wunused -m64 -msse -march=x86-64 -pipe

As mentioned on #45, following #31, the Makefile-backed Linux build on the development branch has been slightly overhauled, including building in a Docker container that provides somewhat-tighter controls of our toolchain. In this case, the Dockerfile in engine/compilers/Make-{32,64}bit/ pins an Ubuntu 20.04 build environment, and uses the distro-default build-essential packages.
This loosely pins us to the following build of GCC:

casey on WATERFALCON in ~ 
at 09:02:55 🍀 docker run -it torque2d-linux64-build-env
root@5998068a57ba:/# g++ --version
g++ (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[nahkhiir]

This issue is due to the header guard _HASHTABLE_H defined in hashTable.h.

That header guard is a reserved identifier in the gcc standard library (code here in gcc repository - line 31).

Renaming the header guard in hashTable.h allows a full build with -std=c++17.

For the revised name I added a trailing underscore i.e. _HASHTABLE_H_ which also brings this header guard into line with the Torque code style guidelines.

[nahkhiir]

I have submitted a pull request for this.