[Predef-contribute] Adding MCST Elbrus architecture and MCST lcc compiler

[Alibek O. <a1b...@gm...>]

Hello!

I suggest adding Elbrus architecture predefined macros and it's,
unfortunately, proprietary compiler to the list. There is also a Clang port
but it's in beta for now.

As LCC and MCST lcc have the same name but are completely different
compilers, I will refer to Elbrus compiler as MCST lcc.

Elbrus can be detected by macros:
* __e2k__ -- defined by MCST lcc and Clang.
* __iset__ -- defined by MCST lcc, value equals version of the ISA.
* __e2k64__, __elbrus64__, _ARCH_E2K64 -- defined by Clang with 64-bit mode.
* __elbrus__, __ELBRUS__, _ARCH_E2K -- defined by Clang in both 32 and
64-bit mode.

There are also model-specific macros(like __elbrus_8c2__ or
__elbrus_1cplus__) but I haven't seen them used in the wild.

MCST lcc can be detected by macros:
* __LCC__ -- defined by every version of MCST lcc. Value equals to the
major version of the compiler, e.g. for 1.25.14 it equals 125.
* __LCC_MINOR__ -- defined by every version of MCST lcc. Value equals to
the minor version of the compiler, e.g. for 1.25.14 it equals 14.
* __MCST__ -- defined by MCST lcc since 1.25, as opposed to __LCC__, which
has a conflict with Little C Compiler

This compiler also sets EDG macros, as it uses it's frontend, and GCC
macros, as it claims compatibility with GCC.

Thanks,
a1batross.