Impossible to compile on Alpine Linux(musl libc)

Created by: illiliti

-DMEMORY_ALLOCATOR=standard should be specified by default for musl libc because it doesn't support custom memory allocators

Non-portable functions should be removed or replaced with alternatives(e.g libexecinfo)

• src/xrCore/FS_internal.h src/xrCore/LocatorAPI.cpp
  • sys_errlist glibcism
• src/xrCore/xrDebug.cpp
  • execinfo.h glibcism
• src/xrCore/_math.cpp
  • fpu_control.h glibcism

Cmake generates invalid <build directory>/src/xrGame/cotire/xrGame_C_prefix.c with missing includes

#include <string.h>
#include <stddef.h>
#include <stdlib.h>

Cmake should search include path for directfb in /usr/include/directfb too, not just /usr/include