Add system's polling infrastructure to be notified whenever a
file descriptor is ready to be read from or written to.
Adds a few classes:
* Poller, as an interface to epoll()
* Pollable, as an interface to a file descriptor
Revert these commits:
"AP_Common: gcc 4.9.2 behaves differently from 4.9.3"
"AP_Common: this workaround for missing/cmath is also needed for gcc 4.9.3"
This breaks the build for PX4. The change is related to the libc, not
the compiler version. We have an workaround there based on compiler
version just because it's usual to have a more recent libc version when
you have a recent compiler.
The way the build was fixed for gcc >= 5.3 breaks the build for older
compiler versions on waf. Fix this by ifdef'ing for WAF_BUILD and
checking the compiler version.
This header is used by waf to contain the generated version macros,
particularly using the git hash. For waf it's better to be in a separate
header since it then can keep track of changes on it a trigger
recompilation.
For the make build system, a dummy ap_version.h file has been added in
the missing/ folder so both implementations can co-exist.
Add a cstddef header to allow using std::nullptr_t with those toolchains
that don't provide it. The idea is to make these platforms to use our
wrapper header (see https://gcc.gnu.org/onlinedocs/cpp/Wrapper-Headers.html)
and then we add the missing bits to the header.
Andrew Tridgell
Pierre Kancir
Lucas De Marchi
Leandro Pereira
Siddharth Bharat Purohit
Francisco Ferreira
Ricardo de Almeida Gonzaga