The command flags '--with-arch' and '--with-abi' can be dropped when
'--enable-multilib' exists.

See: https://github.com/riscv/riscv-gnu-toolchain#installation-linux-multilib

Reported Error Message:

2020-07-22T02:00:47.8864240Z make[2]: fork: Cannot allocate memory
2020-07-22T02:01:47.9284265Z g++-8: fatal error: Killed signal terminated program cc1plus
2020-07-22T02:02:17.4876066Z compilation terminated.
2020-07-22T02:02:40.6296529Z make[2]: *** [lra-constraints.o] Error 1
2020-07-22T02:02:40.6515874Z make[2]: *** Waiting for unfinished jobs....
2020-07-22T02:04:41.7284297Z g++-8: fatal error: Killed signal terminated program cc1plus
2020-07-22T02:04:42.4265291Z compilation terminated.

 remove libgmp-dev  libmpc-dev libmpfr-dev  from install, otherwise it will not download extra gcc external library by set NEED_GCC_EXTERNAL_LIBRARIES=true, which will cause the build for gcc will not work cross machine which don't has same version library of  libgmp-dev  libmpc-dev libmpfr-dev

First workable github workflow script, it can build and works for the following OSes:

* Ubuntu 16.04
* Windows
* MAC OS

Signed-off-by: Huaqi Fang <578567190@qq.com>

New testsuite filter scheme

Bump and fix newlib

 - This fix gcc testsuite: gcc.dg/torture/pr68264.c

 - newlib was default to XOPEN MODE before 2018/12/6[1], but newlib
   decide to remove XOPEN mode SVID3 mode, and change the default IEEE
   mode.

 - The problem is IEEE won't set errno on several math function, so
   build with POSIX mode would be better for newlib.

 - For newlib nano, we might able to build with _IEEE_LIBM in future
   to reduce code size, and improve performance.

[1] https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;a=commit;h=b14a879d85b171960df789ac8ba2332004f838e0

Rv32 qemu glibc update

Drop riscv-qemu, add upstream qemu, and fix one Makefile reference.

Bump newlib

Update to gdb-8.3 with our local sim port added.

Use -O2 for newlib and -Os for newlib nano.

Bump dejagnu to include newlib-nano testsuite support.