What changed in EDuke32, build by build

Fix STARTUP_WINDOW=0 on Windows so that the resource objects are built, but the editor's startup window is not. DONT_BUILD.

Extend STARTUP_WINDOW to GTK. DONT_BUILD.

Fold OSX_STARTUPWINDOW into STARTUP_WINDOW. DONT_BUILD.

Remove -fno-pic from everywhere. This should fix building on Ubuntu 16.10 and any other platform that has PIE enabled.

Revert r5864 and move some code introduced in r5762 to a later Mac-only block so that architecture detection is not broken on Linux.

Allow an invocation like `make CC=clang-3.8` to work properly.

Only apply $(ARCH) processing code on Macs.

Switch the detection order of OPTOPT flags so that i386 is checked after x86_64. This ensures full compatibility for fat OS X binaries built using ARCH="-arch i386 -arch x86_64".

Create GTK *_banner.c files in obj/ subfolders instead of rsrc/ so that they don't need separate cleanup rules.

Make Objective-C code build as Objective-C++ when we build C code as C++.

Add extra optimization defaults for OS X builds since all Intel Macs are guaranteed certain features due to the time of their debut.

Clean up handling of architectures.

Convert object lists to an escaped multi-line format for better diffing.

Add some missing dependencies on the folders in which objects are created.

Add L_CXXONLYFLAGS, and use it to pass "-static-libstdc++" on Windows.

Remove STATICSTDCPP variable.

Rename "CPPONLYFLAGS" variable to "CXXONLYFLAGS", since "CPPFLAGS" traditionaly refers to the C preprocessor, not C++.