* FIXED: rexm's makefile and default paths

Fixed a windows only backslash in
rexm's makefile causing build errors on macOS and linux

Added unix paths to rexm for better compatibility

* Update rexm.c

Readded the fall-through in OP_CREATE

Added some safety checks to UpdateRequiredFiles() so it plays nicely outside of the raylib.com context (would segfault previously)