SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
GCC will insert various calls to pthread functions when compiling
C++ code with static initializers, even when the user doesn't link
their program against libpthread explicitly.
This is used to make static initializers thread-safe, e.g. when
building a library that does not itself use thread functionality
and thus does not link against libpthread - but is intended to
be used with other code that does use libpthread explicitly.
This makes these symbols available in libc.
GCC installs a fixed version of the <limits.h> header as per https://gcc.gnu.org/onlinedocs/gcc/Fixed-Headers.html.
The fixed header doesn't include the target's <limits.h> which in turn means that some definitions (such as PATH_MAX)
aren't available. This change requires rebuilding the toolchain (Toolchain/BuildIt.sh).
This fixes the flatbuffers port.
The commit also removes some non-standard defines (U*_MIN) which don't appear to be used
anywhere. By definition they're always 0 though so they're not strictly necessary.
This required a bit of rearchitecture, as pthread_atfork() required a
mutex, and duplicating a mutex impl for it was silly.
As such, this patch moves some standalone bits of pthread into LibC and
uses those to implement atfork().
It should be noted that for programs that don't use atfork(), this
mechanism only costs two atomic loads (as opposed to the normal mutex
lock+unlock) :^)
