Changes

Summary

1. update prereqs (details)
2. Update compiler support for GCC >=10 (details)
3. more os2 work, don't add libc, use own is_absolute and absolute code (details)

Commit 64f908cc3608e9e77949601029c517cce380d2c8 by rushfan update prereqs
	builds/os2/prereq.cmd
Commit 44cd644fad2068aea330b286d3f414dfdc95af19 by rushfan Update compiler support for GCC >=10
	deps/cl345/tools/ccopts.sh (diff)
Commit a7c34f9c52448dffb285e901c3740df516551361 by rushfan more os2 work, don't add libc, use own is_absolute and absolute code
	CMakeLists.txt (diff)
	core/file.h (diff)
	bbs/make_abs_cmd_os2.cpp (diff)
	cmake/Common.cmake (diff)
	core/CMakeLists.txt (diff)
	core_test/file_helper.cpp (diff)
	core/file.cpp (diff)