[8u] RFR: JDK-8164041: support old pre-c++11 toolchains and ucLibc

[Andrey Petushkov]

Hi All,

We met a necessity to support an older kind of gcc toolchain which does not fully conform to c++ 11 and in particular do not have __atomic API as well as have some other peculiarities. In addition the support of ucLibc was desired.

The resulting changes are here: http://cr.openjdk.java.net/~apetushkov/8164041/webrev/ <http://cr.openjdk.java.net/~apetushkov/8164041/webrev/>
Checked with running on OpenWRT-based distribution

When implementing the replacement code we also chosen to always use the assembly implementation and not builtins because:
- there is no harm, the assembly is no worse than that gcc can generate
- the code is more clear
- there is no reliable way to determine if gcc has flaws or not, so the detection directives look really ugly

Thanks,
Andrey