build with MRB_GC_FIXED_ARENA.
Automatically detect toolchain if it is visualcpp, and hence we drop vs2010.rake altogether - it’s no longer needed.
Merge pull request #1591 from iij/pr-fixed-arena-on-travis

build with MRB_GC_FIXED_ARENA on travis
Merge pull request #1592 from perlun/auto-toolchain

Automatically detect toolchain if it is visualcpp, and hence we drop vs2010.rake altogether - it’s no longer needed.
Merge branch 'master' into iij