getopt() in the FLAT build environment is not thread safe. This is because global variables that are process-specific in Unix are truly global in the FLAT build. Moving the getopt() variables into TLS resolves this issue.
No side-effects are expected other than to getopt()
Tested with sim:nsh
Squashed commit of the following:
libs/libxx: Fix some confusing in naming. If the directory is called libxx, then the library must be libxx.a (unless perhaps LIBCXX is selected).
libs/: Fix paths in moved library directories.
libs: Brute force move of libc, libnx, and libxx to libs. Cannot yet build it in that configuration.
