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.
Francisco Ferreira
Lucas De Marchi
Andrew Tridgell
Ricardo de Almeida Gonzaga