Some issues with the Makefile

See merge request !1553

If a variable is defined as in 'make CC=gcc-10', then that
definition overrides anything other definition in the
Makefile.

After a checkout from before revision, old directories
such as bin/Linux64 only remain if untracked files exist
within. This may be confusing to the user. They may even
use an outdated executable if it is one of those untracked
files.

Hooklib refactor

See merge request STJr/SRB2!1307

This is for MSYS2, which requires unix shell commands.

File function is not supported < Make 4.2.

# Conflicts:
#	src/lua_hook.h
#	src/lua_hooklib.c

Let Lua access key presses, mouse properties, and joystick properties

See merge request !1436

# Conflicts:
#   src/lua_script.c

Restore toggle for Robo-Hood to not jump away from nearby players.

See merge request STJr/SRB2!1548

Ignore a linedef tag of 0 when using linedef action 96.

See merge request STJr/SRB2!1543

With added textual contrast.

NOOBJDUMP=1 and NOUPX=1 have been removed. Make 'dump'
target to disassemble. UPX=upx to compress executable.

Setting UPX used to cause it to fail. That has been fixed.

Allow P_CheckSight to see through FF_FOG FOFs

See merge request STJr/SRB2!1546

Replace "II" in credits with "2" for consistency

See merge request STJr/SRB2!1547

blame e0a307da